JB wrote:
"It's really weird. I have found myself slipping into France, circa 1917, as if I was working from actual memories. And I have not seen that many WW1 movies!"

Well, you've obviously seen "enough for comics" (to run with the "close enough for comics" phrase a bit further).  ;)

Or you've perfected the time machine and just neglected to tell us...

Memory is a wickedly weird and absolutely fascinating thing in how it can be utterly precise and truthful to a given situation in one case and equally precise but obviously untrue in another.

Salman Rushdie tells an interesting story about the time when India was at war with China (unless my memory fails me this was in the 60s). In his essay "'Errata': or Unreliable Narration in Midnight's Children" (collected in Imaginary Homelands) Rushdie states:
"I myself have a clear memory of having been in India during the China War. I 'remember' how frightened we all were, I 'recall' people making nervy little jokes about needing to buy themselves a Chinese phrase book or two, because the Chinese Army was not expected to stop until it reached Delhi. I also know that I could not possibly have been in India at that time. I was interested to find that even after I found out that my memory was playing tricks my brain simply refused to unscramble itself. It clung to the memory, preferring it to the mere literal happenstance. I thought that was an important lesson to learn."

And I myself have had one sych instance where something I remember has been proven beyond any doubt not to be the case, but where the memory still persists even though I know it's false.