Something popped into my head last night before going to sleep. It goes back to the old marrying the original trilogy to the prequel thing.
Obi-Wan technically didn’t own a droid in the prequels. He was a Jedi and the order had access to droids. He was friendly with them but didn’t take them too seriously. He wouldn’t mourn a decapitated R2 unit like he would a youngling but he also didn’t treat them like furniture.
When he comes across Artoo in episode 4 he may not of expected to see him again. His brain would possibly dismiss the idea that this blue astromech was the same one Padme owned or Anakin had flown with because there were only so many colours and probably millions of units made.
But once Luke mentions Ben’s true name the nagging suspection that the R2 unit was Artoo must have entered his mind as well as the implication that this was the moment when training Luke would be necessary.
So my suggestion is, if possible, add a “Artoo?” to the scene from Ben and have Artoo respond. Maybe just before he says to Luke that doesn’t remember owning a droid.
A bit like him saying to Artoo “I going to pretend to not know what’s going on but I do remember.” an exchange that they would share and the audience would see but went completely over Luke’s head.
Alternatively it could happen while Luke is unconscious but that would mean Ben recognised Artoo right away and deduced the situation immediately which might very well be a Jedi thing. Though he might still suspect an Imperial trap.
If I went back to 1977 and saw such an exchange I would be intrigued by what’s going on. I think that’s a good criteria for changes like this. But it’s probably impossible to do anyway.
Just a thought.