I thought there might be a correlation between serial numbers and firmware revision numbers based on a sample of ten drives I opened and examined, but based on new evidence, there doesn't seem to be any consistency. Regardless of serial number (and regardless of where the drive was manufactured), the firmware could be AAC, AAE, or AAK. I even found a 7200.9 drive instead of a 7200.10 drive inside a red and white Maxtor box (which I expected to be a Maxtor-branded Seagate 7200.10 drive just like all of the others I had seen).
Best of luck to everyone. I hope you get what you're looking for.