If a Pokémon is missing from our gallery, chances are it’s been lost to time for good. If you find “missing” events on other websites, they’re very likely fake, unless they come with proper proof and evidence of authenticity.
That said, Gen 1 and Gen 2 events are essentially just basic templates where only the TID and OT really matter, and those can be easily modified/spoofed with tools like PKHeX.
I’m not sure I understand what you mean.