@mrsconradfisher, @Thehop, my youngest brother also had detailed 'memories' of his adult life, at age 3 or so. He said he was a farm hand, from his tales it would seem before the introduction of farm machinery. That could've been any time up to the 1950s, though. No idea where he got it all from - we lived in the industrial midlands, but I guess older people around us may have told stories from their more rural pasts. He doesn't recall this phase.
I have met my 'other self' and she made a huge difference to my life! She came in to my bar, ordered a drink and we both noticed we were nearly clones. So did everyone else there. We even had the same cackling laugh. We got talking, naturally, and turned out she worked in a field that really interested me. She gave me good advice on how to get started.
We even had the same - very unusual name 😮
I ended up in a career I absolutely loved, similar to hers. I never met her again but here's the glitch: lots of other people did meet her, thinking she was me. Naturally enough, they got miffed when I seemed to be totally blanking them and, if they called her by name, claiming not to know them. Many of these people were clients of mine; it was a problem. Worse still, it seems she had an alcohol issue (even more than I did) so I acquired a reputation for not being where I should have been - and actually was - getting loudly drunk with people who were not connected to my own job. It caused very real problems.
No fucker believed it wasn't me. I found her in a trade directory, but people will rather hang onto their first assumption than accept the unlikely reality. This went on for years. At times I even doubted myself, despite my printed evidence. I was ridiculously grateful when an old friend ran into 'other me' and said he was initially confused, but then realised her style of dress was out of character for me and he'd met my mystery doppelganger!
I did ring her direct line from the trade directory. Someone else picked up, offered to get her, then came back saying "She doesn't want to speak to you and asks you not to call again." Left my number just in case, but nothing. It's an uncanny story all right, but it ain't paranormal 👀