To my knowledge the product serial number and customer exclusive serial number are one in the same. You may be thinking of the salespersons' product codes, which I don't think had anything to do with the production time.
I've made several attempts at decoding the digits, but have concluded that they are only the production numbers. The 2-letter series is most likely how they were time coded, but the distribution lists were never published for public use and branch offices likely didn't keep them. The first letter usually stayed the same during a model's run, while the second likely changed after every 99,999 produced. Further, the corporate records from the early years to the 1980s were apparently discarded when the Old Greenwich factory was shuttered in 1985. I called corporate several years ago and requested the production times for the vintage cleaners but was told that it had no electronic records of the serial numbers prior to the 1980s. Even so, an Aerus dealer informed me that the electronic records only tell them the original sales date. So a cleaner may have been manufactured in one year but not sold until the next; resulting in skewed data.
It would be awesome if an Aerus franchisee would upload the lists. There's probably at least a half dozen of them that have kept their records and either don't realize it, don't care, or don't appreciate how it would promote customer interest and loyalty to the Aerus (Electrolux) brand.
