Board Thread:General Discussion/@comment-26838855-20190803131136/@comment-28529249-20190807235218

Edward Zachary Sunrose wrote: Russos are sticking to the alternate timeline theory (thank god). Steve did not return to that moment on the bench, that's why he doesn't have the Quantum Suit on.

https://www.reddit.com/r/marvelstudios/comments/cn9lbx/were_joe_and_anthony_russo_directors_of_marvel/ew9238h/?context=3

A long standing theory is that Old Man Cap left his new timeline in 2016 when Peggy dies (assuming she still dies in 2016) and waited 7 years in the MCU. I don't buy that. I think, going by what the Russos said, Steve jumped to the main timeline sometime during the final battle or its aftermath, and waited until Young Steve left.

So that would make both official explanations right; Cap lived his life in an alternate timeline, but he returned to the main timeline when his younger self left, creating a loop for Cap's internal chronology. The Quantum Tunnel was destroyed when Thanos passed through it, and so was Luis' van during the battle. The new platform had probably just been made when Cap left, I don't think it's possible for Old Steve to have come back without anyone noticing.

And I don't see how that would make the M&M explanation right. Theirs doesn't involve Cap using the Quantum Tunnel again to come back.

I think we'll just have to deal with the fact that the movie was written one way (M&M) and was filmed and acted using that explanation, but moving forward Marvel will use the Russos' explanation (which likely came about because of Marvel's future plans for the franchise).