>>533945436
>>533944045
>>533942459
My personal Metal Sonic timeline goes
CD>3&K>Chaotix>Fighters>R>Drift 2>Triple Trouble>Mania>Sonic 4 Ep. 2>Heroes>Rivals 2>Current
look at the description for Kai
>>533926628
>sub CPUs were recovered from the body that was destroyed in a previous confrontation
So Metal Sonic was killed off in CD and Kai was his replacement who shows up in the spinoff and handheld games.
I like to think that Kai would then be destroyed for good in Triple Trouble.
Eggman realizing that Metal was his best Sonic copy to date would then bring the OG back with the Phantom Ruby.
Sonic fights him again in Stardust Speedway and beats him once more.
However, this time his body wasn't fully destroyed and was just left on Little Planet
Realizing this, Eggman brings him back yet again in Sonic 4 where he gives him his updated "Modern" design.
The pink orb Metal obtains during Episode Metal not only gave him a powerup, but a consciousness as well, which is why he went on to betray Eggman in Heroes.
After his defeat, Eggman would then reprogram Metal into being a mindless servant for the rest of his artificial life.
Eggman Nega made an improved version of Metal, but that one was either destroyed too or was trapped in the Ifrit dimension.

Multiple versions of robot Sonic duplicates exist, so I can't see why multiple versions of Metal Sonic specifically can't either. This is only counting games though, comics and animations can't fit.