It's not true that the all Neo Geo home cart systems have the same A/V port pinout. The last two revisions of the board crucially lack a sync output, which explains why hooking up these machines to RGB monitors results in a rolling picture. The sync output can easily be restored with an internal mod.
Perhaps the same is true for other consoles and their PCB revisions?
I've never heard that the later Neo systems had no sync output. What serial number did this start on?
I've tested models right up to the 200 or 300ks, and they all had it. So did both CD and the CDZ units.
I always disliked the use serial numbers to account for hardware features: PCB revisions are facts, serials are guesses. However, if you open up a 200k+ you're most likely to find an AES3-6 board, which is the last and more common board revision. I've recently modded an AES3-4 that had a serial 86xxx. I assume that AES3-5 starts at 120-150k. If this is correct the last two revisions (3-5 and 3-6) cover at least half of the existing Neo Geo cart systems. These are the revisions without sync out on the A/V port.
I can't tell anything about CD systems as I've never seen one.