Why are these Mega Man X's different?

[17DaysOlderThanNES]

it's a reprint, simple.

Many popular Genesis games got that treatment via Majesco and are distinguished by having "made in mexico" on the cartridge as well as paper labels vs. the nicer laminated ones.

All games are made in "print runs" in which they make a certain number of copies based on suspected demand and available funds (if made by a smaller company). If the games sell out and retailers/consumers request more, they will have a re-print. The most common form of reprint (and easiest to recognize) is the infamous "Greatest Hits" games.

There are also pirate games, but those usually use wonky artwork from god-knows-where and may alter the title screen or name of the game to try to dodge copyright infringement identification.