Limey

married is married,

It absolutely impacts the k-1. In Islam, signing the marriage contract and having an Islamic marriage "ceremony" makes you married in the eyes of U.S. immigration. My husband is Muslim and we were engaged and married in Jordan, been there, done that. It does not matter if anything was registered or not. You will be married after the ceremony. Period. Don't do it. 

Do what you have to do to hand deliver. Too busy for that may come to bite you later. Ball's in your court. I wouldn't send it. Hand deliver it yourself. 

VJ is full of RapidVisa horror stories

Unless a case is complicated, they all do the same thing......fill in forms with information YOU have to provide. ...and submit the forms.  It is extremely expensive administrative work. 

I've done a lot of traveling and on occasions I've had several vaccinations in the same day. It never caused me any problems. The biggest issue is that some of them require 2 or 3 shots over a period of a few weeks and you're not fully vaccinated until you've had them all. So I'd get her to go to the doctor as soon as possible, and also get a timeline for when the 2nd and 3rd (if required) can be given.

Overlapping relationships definitely isn't a problem. My wife was married when I first met her and when we got together she was separated but not divorced. Had to wait a while to file k1 because we were waiting for the divorce (there are separation requirements in NC). Its not a red flag - if anything the extra waiting time and process involved tends to demonstrate some genuine substance between your relationship, which is a positive.

Age difference can be a negative, but its only part of a whole load of things that will be looked at. With the history of your relationship, the face to face meetings, the fact that you first met in a work environment, etc, etc  you shouldn't have any problems.

I've done a lot of traveling and on occasions I've had several vaccinations in the same day. It never caused me any problems. The biggest issue is that some of them require 2 or 3 shots over a period of a few weeks and you're not fully vaccinated until you've had them all. So I'd get her to go to the doctor as soon as possible, and also get a timeline for when the 2nd and 3rd (if required) can be given.

Overlapping relationships definitely isn't a problem. My wife was married when I first met her and when we got together she was separated but not divorced. Had to wait a while to file k1 because we were waiting for the divorce (there are separation requirements in NC). Its not a red flag - if anything the extra waiting time and process involved tends to demonstrate some genuine substance between your relationship, which is a positive.

Age difference can be a negative, but its only part of a whole load of things that will be looked at. With the history of your relationship, the face to face meetings, the fact that you first met in a work environment, etc, etc  you shouldn't have any problems.

Overlapping relationships definitely isn't a problem. My wife was married when I first met her and when we got together she was separated but not divorced. Had to wait a while to file k1 because we were waiting for the divorce (there are separation requirements in NC). Its not a red flag - if anything the extra waiting time and process involved tends to demonstrate some genuine substance between your relationship, which is a positive.

Age difference can be a negative, but its only part of a whole load of things that will be looked at. With the history of your relationship, the face to face meetings, the fact that you first met in a work environment, etc, etc  you shouldn't have any problems.

She was here in July, and Covid was the one vaccine she got. And thank god because her daughter and dad got covid while she was here and she returned to a house full of Covid and never got sick. Hell of a vaccine! 

You can add mandatory CoVID vaccines to that list https://www.cdc.gov/immigrantrefugeehealth/civil-surgeons/covid-19-technical-instructions.html

Last month, I had three vaccines for seven different diseases done on the same day: TDAP, MMR and varicella. I had no side effects and found it amusing to have three different bandaids on my arms for a day.
 
It's also normal for kids to have had multiple vaccines done during doctor visits without any problems.
 
Source: https://www.cdc.gov/vaccinesafety/concerns/multiple-vaccines-immunity.html

Everything went fine for us. We did receive an RFE but it was a one-off -- the officer who cited me for my DUI accidentally checked the box that my marital status was divorced so they were wondering if I had every been married... completely random as I have never been married.
 
At the end of the day if you disclose absolutely all information you have available and statements from the courts you should be okay. 

Nigeria is in a league of its own when it comes to US marriage visa fraud.  Many K-1s are denied in Lagos.
 
You will need to front load that petition with LOTS of evidence, and honestly, I would advise you to hold off until you have another visit together.  You might be much better off marrying and petitioning for a spousal visa instead.

It won't affect anything, other than giving you another face to face meeting (that's a good thing).
 
After a few too many trips to the USA I did a Canada meet up with my now wife soon after we'd filed for the k1 (got to see some of my Canadian relatives too). During my k1 interview in London the lady interviewing me asked if we'd met again since filing the k1 and I said a couple of times, and mentioned that one of those trips was Canada because US immigration had given me a finger-wagging over the frequency of my US trips on a previous visit. She laughed, but didn't ask any more about it and I was approved with no issues.

It won't affect anything, other than giving you another face to face meeting (that's a good thing).
 
After a few too many trips to the USA I did a Canada meet up with my now wife soon after we'd filed for the k1 (got to see some of my Canadian relatives too). During my k1 interview in London the lady interviewing me asked if we'd met again since filing the k1 and I said a couple of times, and mentioned that one of those trips was Canada because US immigration had given me a finger-wagging over the frequency of my US trips on a previous visit. She laughed, but didn't ask any more about it and I was approved with no issues.

My ex fiancee, now wife, came here on K1 from Ukraine. While waiting for K1, we lived in Tijuana, Mexico all this time. She closed down her law firm in Ukraine. I rented a nice apartment (it is cheap compared to San Diego and really nice if you pick right neighborhood). I have global pass and commuted every day through the border, while maintaining my place in San Diego. When I129 f got approved, we moved to her place in Ukraine for 2 months and waited for the interview. When interview took place, it was a huge plus. No red flags. It will only show your commitment. 

80 days is longer that many people have spent together before filing for k1. Its not a problem. Also NZ would be a low fraud country, a rich developed country - the incentive for a kiwi to perpetuate a fraud to get to the US is much lower than for some other parts of the world. So long as you have reasonable documentation to show you've met within the 2 years you'll be fine.

In terms of first meeting - we just included a brief paragraph within the form where it asked how we met (ie location - bar, dates, circumstances). I honestly don't think they are that bothered about the details, just a basic idea (was it in person, or on the internet, was it a dating site where you're specifically looking for someone, etc). We tried to keep our application as concise as possible - make it easy for the person working on it to find the important and required documents, so we chose not to overload with chat logs and other documents that weren't asked for. Good luck!

As it relates to circumstances of meeting,  look at the size of the space provided on the form for your response.  This indicates how long they expect your response to be.

As always with entry into the US, its going to depend on the officer that you come up against at the border.
 
After making my first 3 trips over a period of 9 months (around 9 weeks in total spent in US) I was stopped at the border for my next trip that was scheduled to be just under 4 weeks. The officer was not interested at all in what ties I had to my home country. His issue was that I was spending too much time in the US and effectively trying to live there on a tourist visa. I said that I believed it was okay to spend up to 50% of the time in the US but he disagreed and said that there is no such thing as a "visiting my girlfriend" visa and that I needed something more permanent. I was pretty sure he was going to send me home.
 
I said that I'd lived in the US previously on a J1 years ago, and had visited many times before and since that time and I'd never overstayed and always respected US immigration laws. I explained that we would apply for a k1 soon but that we were waiting for my fiancee's divorce to be completed and that we couldn't apply until that time. At this point I could sense his mood improving a little - the mention of the k1 seemed to help, and he granted me entry to the country but said that I should leave it a while until returning. For my next trip a few months later we met up in Canada instead so I could avoid a US entry, but I had no further problems with US visits after that (traveling with a k1 in progress by this time).
 
As I said, its all going to depend on the officer at the border. My experience is that even if you can show good ties to home (which you don't seem to have) there can still be problems entering the US if you've spent significant time there in the recent past, and/or are entering for a long duration stay. But there are plenty of cases here where people have had no issues at all.

What do you mean by a visa stamp?
 
1. The date of expiration in the visa,
or
 
2. The stamp CBP put in the passport page with an entry date and an “admitted until” date.  
 
 
For the benefit of others facing this predicament: You have married somewhere that doesn’t require an SSN.  And a place with available appointments.  Like Vegas or the Utah Zoom Marruage.  
 
 
if you got married before the I-94’s authorized stay expired then you are permitted to file I-485 to adjust status.  The period of unauthorized presence will be forgiven by USCIS. 
 
However the rest of DHS, namely CBP and ICE, do not have to forgive.  
 
The alien spouse should avoid encounters with law enforcement, airports, and the border (stay over 100 miles away) at least until the AOS package is filed.  File the package with proof of mailing. 
 
Even after the AOS package is filed, ICE can still make life painful until there is a decision on the I-485.  

No, it isn't too late.  But as she is now out of status, she could potentially be deported.  If I were you, I'd order the marriage certificate as soon as it is available.  While you're waiting for that, get everything else ready to send the package out asap.
 
And because you live in a border state, be aware that she may want to lay low around border checkpoints (I'm not sure what they're called - the ones that are *near* borders, but not actual border crossings) until you get the NOA1 for the AOS, at which point she will be under "authorized stay" while waiting.  Don't forget to apply for the EAD/AP concurrently with the AOS - it's free.

What country are we talking about? There are some consulates where even attempting to rectify this is not gonna work. So if you tell us the country, we can tailor our responses @Jmsamonte
 
My summary. OP is not telling us the truth. Additionally, I suspect, from language, that it is the immigrant who is posting in an attempt to find answers to their lies.
OP, the chickens have come home to roost. 
 
I am out.

OP,  you just shot yourself. Your story keeps changing.
I am out. I am not gonna spend time chasing for truth. Let a lawyer do that. 
All the best.