You raise a great point, Lana.

I wonder what Vito knew, if anything, about the Vegas interaction. I guess it depends on how "semi-retired" he was.

Of course, it's also possible that Vito didn't consider Fredo's action taking sides against the Family, although it's hard to imagine he would have been happy about Fredo expressing an opinion in front of others.

But he might have dismissed it as Fredo being "well..." and, understanding that Fredo had no real role in the Family, not addressed it since he didn't view Fredo as a potential threat/weakness.