Wow, that's cool! I never knew that. Do you have a list of all of the manufacturer codes by chance? I'd be interested in seeing which companies tended to make more reliable systems (I see more EFA systems working than whoever made the S and B systems, at least with Game Gears).
I'm not familiar enough with the GG to say, but doesn't that machine suffer from bad caps universally?
If they were reserved for later mobos, I'd think those mobos would have to be different in some way? Or like you say, they assembled units for Australia separately, a bit later, so they ended up using mobos made later. ? Of course if you end up with hundreds of similar cases for a certain region, it's probably not a coincidence.
I think they just planned on producing x number of units for each region in advance, and then produced the ones with higher priority first, eg. Japan.
It's a bit muddy because some production runs alternate between, for example, PAL and JP units very often. Some between PAL, JP, and USA units. It is unclear yet if those were two runs running in parallel, or if they indeed switched types every few thousand units or so. I have yet to see any serial number collisions yet, but that could just be due to a lack of samples on my part.
I need to streamline the site at some point to make it simpler to add serials, perhaps add some way for users to submit serials, so the db can grow exponentially faster... lot of work, not enough time to do so.
Either way, to determine the manufacturing date the units also need to be opened.