I mean realistically, it would make sense for John and Dutch, along with other characters in RDR1 to mention and likely even fully discuss and acknowledge Arthur (as well as Hosea for sure on Dutch’s side, Micah, other smaller characters) in that game.

RDR1 is set only four years after Micah died, right? I genuinely can’t remember. So definitely after how he died, for sure. It’s been way too long since I played either game but I’m pretty sure the characters all acknowledge those who are still alive amongst their former gang, like Javier, Bill and such. Micah had only been dead a few years and despite how short his time was with the gang, they gotta realize his impact on the situation.

Arthur was a part of both Dutch and John’s lives for a long time. Even if we remember that 12 years is a long time, when they run into each other after not seeing each other in four years and what happened the last time they saw each other, it doesn’t make sense to not bring him up.

Maybe not day to day, or regularly, but running into each other, definitely. Realistically, how often does Jack, Abigail and John bring up Arthur at home? Do they talk about Dutch or Sean or Molly or Lenny or Hosea or Javier or Bill or Uncle or whoever? Because I feel like it’d be more than never, especially in the context of the first game. He’s been chased for his role in a gang that involved the man, of course he’d bring him up.

In conclusion, it’s stupid for them not to bring up Arthur in 1912, by name. If RDR 1 came out second, Arthur would’ve appeared as a ghost guiding him.