So an update my E-Gate experience. Entered in the country 2/23 via E-gate in T2 MEX. Got the slip. Left last Saturday 3/18. I tried doing the whole QR Code, registered, my arrival was not registered online so I could not print out anything.
Since I had the time, I went to the local Immigration office to talk to them, their response was "meh, it has the registration info on the ticket, just use that"
(As an aside, I had a valid stamp from a November entry good until May).
Upon check-in, I showed the ticket to the check-in agent, and that was it. I shoved the ticket in my pocket and was never asked for it again. During the security interview to my JFK bound flight, they didnt ask for it, or even check my passport for my stamp.