I think many people figured out the Missingno shoreline kept some form of “last encounter table” in it, so I wouldn’t be surprised some people may have tried to go there right after Mewtwo to chance themselves at more.
Unfortunately we do have that info nowadays, and we know that doesn’t work.
You could do it with one copy probably. But this was pre-internet so harder to know about the glitches and such.
I think many people figured out the Missingno shoreline kept some form of “last encounter table” in it, so I wouldn’t be surprised some people may have tried to go there right after Mewtwo to chance themselves at more.
Unfortunately we do have that info nowadays, and we know that doesn’t work.
Don’t forget to try and move the truck, there’s a Mew under there I promise, my cousin got it!