In The Winter Soldier, Steve visits a museum exhibit about Captain America, where he watches a video featuring a post-WWII Peggy talking about her life.
The following post contains SPOILERS for Avengers: Endgame that might possibly make your head hurt from considering all the time travel paradoxes.
On the other hand, the way Peggy describes her husband here it really doesn’t sound like how she would talk about Cap?
I also don’t understand how this squares with the rules of time travel that Endgame explicitly lays out?