GaN2

They can certainly ask you for 2018 transcripts ,usually they are available after one week you file your taxes but in case if itsn't available by that time ,you can take W2's and tax returns and explain them that transcripts aren't available yet. I have the same situation ,i filled my taxes in February but IRS send me letter this month and that they need my health insurance form to process it  so i requested them that i need to have those tax transcripts available by first week of May or they issue me a letter stating one so they send me a letter for immigration  stating why my transcripts aren't available in case they ask one . If your sponser income is good in last 2-3 years or in the last 3 year tax transcripts ,there is very likely they don't even ask you for transcripts. Usually they ask who have low income just to verify if he is still earning the minimum require. 

I actually have no idea if he physically mailed it, I think he filled online since the Tax Transcript from the last 3 years were downloaded. I will ask him if he have available the transcripts, otherwise I will ask him for the tax return and the 2018 W2. Thank you!