There were a few variations. For the nes you could get an adaptor that took a nes game (for the lockout chip) and a famicom game, allowing you to play famicom

There were a few variations. For the nes you could get an adaptor that took a nes game (for the lockout chip) and a famicom game, allowing you to play famicom games, that didn't have lock out chips. A few pirate/ unlicensed games went this route also. I've seen a similar thing for the snes. I believe the super famicom had a lock out, so cant remember if this was required for those.