Yep. Its either a random system a la Rolex or more likely a system that uses A then a 5 or 6 digit number. Omega hit 100K late last year and rather than add a digit started again with an A.
The reason why I think it isn't a random serial is that all I have seen start A...
Using letters your level of entropy increases very significantly. Omega won’t run out of serial numbers before we go back to sticks and stones with 8 characters of 0-9 and A-Z.
The use of letters and numbers have been used in vehicle ID no's for ages, the 8th character from the right is the model year, i.e. K=2020, L=2021 (Q and O will be skipped).
This makes sense - at least they haven’t gone the way of the reference numbers which supersized when they went from, for example, 3570.50 to 311.30.42.30.01.005 😵💫