This next post ties to one of the reasons why I created this thread
Bootlegs as far as I heard have been around since at least the early 1990's and maybe sooner. that is why I heard Nintendo made their
"official seal of quality" on all Nintendo licensed cartridges in the United States. starting with the Nintendo Entertainment System. and ending when the came out GameCube, I think. Also far the circuit board is concerned, people say something about the Black battery goop. On the insides of NES or SNES? I can't remember correctly. that it is a common fake cartridge, But that may or may not be the case.
I believe sometimes shops might only replace the battery. But I never heard of anyone ever doing that.
But like some already said on here a lot of bootlegs. Have a vary close resemblance. To the real thing. Including games with a missing or distorted Nintendo Official Seal Of Quality. Found on some Nintendo cartridge games.
And sometimes the chips are even identical to the real thing. Meaning, you may need to do extensive research on every cartridge you own, (it can be a lot of work to do that even with the internet) and sometimes only an expert sometimes can tell you if the inside of the cartridge is fake or not.
Also CD/DVD/Bluray fakes I think, have a paper sticker label covering the whole disc itself so if you have a bootleg disc game it may have a paper label on it. If it is a fake.
I have a copy of Legend Of Zelda for the NES and the game still saves, but I never opened it up so I don't know if that is a fake or not because the cartridge outside is shiny golden and the label is badly torn