The K1 Visa expires 6 months after it was issued, although it only lasts for 90 days after you entered the USA (I-94)

In the form I-485, Part 1, they say: Expires on:

Is that the I-94 or the K1 Visa date?

I put the K1 visa date

They want the I-94 expiration date, since the K1 expiration date doesn't matter anymore, just the 90 days since POE, so it's whatever they stamped on your I-94 (they stamped the same date on my passport as well).

ops.. I think they didn't even pay attention to mine then

Probably not, Lisz.

The date on my I-94 is not the same date as in my visa. My visa will "expire" 3 months after my I-94.

That's just the expiration date before which you must enter USA. So once you enter USA that date no longer matters, what will matter is the I-94 expiration date, the date before which you must get married.

I know that... I think that I wanted to "show" that the dates are not the same and that they really do not pay atention on your visa expiration date.

Yep.