User:SOTO/Forum Archive/The Reference Desk/@comment-5545417-20131116122722/@comment-188432-20131119081644

• The Five Doctors provides evidence that the first three Doctors remember The Three Doctors.
• There's no evidence that Two forgets having met Six in The Two Doctors. For that matter, there's no strong direct evidence that One, Two and Three forget Five in Five. They seem to leave with their memories intact, but for some reason fans recollect wrongly that all their memories are wiped. (I wonder if that's an impression given by the novelisation; it's certainly nothing to do with the episode as aired.)
• I'm pretty sure Five remembers Seven following the events of Cold Fusion. Could be wrong though.
• Time & Time Again has no direct contact between incarnations that I recall, so there's nothing to forget or remember. However, it's all about healing an alternate reality anyway.
• The Eight Doctors definitely has younger Doctors remembering older Doctors. Notably, Two gets a pep talk from Eight in which Two is convinced to turn himself in to the Time Lords despite every fibre of his being screaming otherwise.
• Happy Deathday i only ambiguously real; it can be interpreted as Izzy Sinclair playing a video game.
• I'm pretty sure all memories are retained at the end of The Sirens of Time — but please don't make me listen to it to find out for sure!
• Zagreus: Seriously, no one, not even the producers, really know what this story was about. I'm not being facetious.
• The Four Doctors - The story depends on the Doctors remembering each other's footsteps, but they don't actually cross paths, as I recall.

Most multi-Doctor stories in other media are more like The Four Doctors than The Three Doctors. That is, they're about multiple Doctors working on the same problem but not directly crossing paths. So of course they actually remember what happened to their past selves. Since their past selves never meet their future selves, there's no memory of their older selves to forget.

The question I'd have is whether there's any story in which the Doctor's memories are clearly and unambiguously stripped from him. I can't think of one, even though I know it's always said by fans that this happens in The Five Doctors.