It is pretty straight forward:
Defender => Defender
Stargate Rev0 <=> Stargate Rev0
Stargate RevB <=> Joust <=> Robotron <=> Sinistar <=> Splat!
Bubbles<=>Bubbles
Stargate Rev0 has two versions. A real Early version without the daughter card and the later version with the daughter card. Both boards need a mod to be able to run later games. But the Stargate ROM card wil run on all versions.
Rev B came out with Robotron (and was retrofitted to the very end of the Stargate run).
Rev C came out mid-Joust.
Rev D came out late-Joust, before Sinistar. Splat! was the last on this board set
Bubbles uses 16bit CMOS so they changed the ROM cable to avoid confusion. You can run any of the games (except Defender) on a Bubbles ROM card (you need Special chip 2's for Splat!).
If you plug a Defender ROM board on a later MPU board, it will look dead.
If you plug any of the other ROM boards on a Defender MPU board, it will look dead.
If you plug any of the other ROM boards on a Bubbles MPU board, it will look dead.
If you plug a Bubbles ROM board on any but a Bubbles MPU board, it will look dead.
Simple, huh?
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