The second Doctor remembered Omega as we learned in The Five Doctors and the tenth Doctor took the memory of the fifth Doctor to solve the problme in Time Crash. There's realyl very little evidence to support the idea that they can't remember meeting their previous selves.
But what kind of a story would The Five Doctors have been if they'd remembered? All the First Doctor would have had to do is say, "Oh, this is no problem. We have to do x, y, and z and meet my other selves here, here, and here, and the whole thing will be solved in time for tea."
The only thing stopping them from doing that would be the determination to not alter their own personal time line. After all, just because you know something will succeed in the future, that doesn't mean you're not excused from doing everything that leads up to it.