Timeline for the Narrations.
I started wondering when Ace and Nickey were telling the story about their time in Vegas, which would be the narration for the movie. Then it occurred to me that they weren't telling the story at the same time.
Ace was probably in the mid 90's, since he talks about ending up right back where he started, and he seemed at peace with it.
Nickey was probably doing his in 1983, which is why it abruptly cuts off at his death.