Serial Number Epoch rollover
We use a little tool internally to automatically decode the Apple devices in our fleet by their serial number. Their serial numbering schema has been stable across all their devices for 10 years but the end of 2019 marked a “rollover” event where they were running out. Looks like they’ve reset everything back to 2010 as our latest device with a build date of week 1 in 2020 has the same date code as a 2010 device.
To recap… the system is:
Digits 1-3: Factory Code
Digit 4: Year and Half starting with C (2010, 1st Half) and going to Z (2019, 2nd Half)
Digit 5: Manufacturing week (1-28 or 29-52 depending on Digit 4)
Digits 6-8: Unit ID (the actual serial number of the machine made that week)
Digits 9-12: Model Code
So with Z marking the end of 2019, 2nd half, our latest device has a C which indicates that they seem to be starting over.