User:SOTO/Forum Archive/The Reference Desk/@comment-5545417-20131116122722/@comment-26975268-20131201170046

"There's something I don't understand," Cwej said.

"Hmmm?"

"Well, if he’s your future self, why don't you remember all this from first time round?"

"Does everything have to have a reason?" Forrester asked. "Perhaps it's magic."

"No, no," the fifth Doctor said, "the rules of time travel are very precise, and Mr Cwej here has a good point. Now, on both occasions that we met Omega, that was straightforward Blinovitch Conservation."

"That was true all three times, yes, but it doesn't apply here," the other Doctor noted from underneath the console.

"Yes, yes, I know that. Now, Zodin erased our brains with mind rubbers."

"I remember it well."

"But that hasn't happened this time? The crashed TARDIS might have had misphased Relativity Displacers."

"It might," the seventh Doctor conceded, "but it didn't."

"Tachyon Backflush?" the fifth Doctor suggested. Chris sniggered. "Sorry – it's just that it sounds rude.’ Forrester shook her head disbelievingly. Her Doctor stood, brushing himself off and taking his umbrella back from his past self.

The fifth Doctor straightened. "There is another possibility."

"Go on."

"You do remember. You've remembered all along."

So, as Czech pointed out, this is very much a Time Crash in that no memory loss occurs. Memory loss is not in fact an automatic process every time different incarnations meet, according to this book. Instead, it's very much dependant on the situation, and each meeting either has a different reason for the loss of memory, or memory is retained.