I was also able to confirm the model year is the first two numbers of the S/N. The other numbers I am not sure but could be date codes for production?
Thanks
Some times it is the first didgit only that refer to the year, some times it is the first two, some times the year is there (4-didgit) - and on really old ones there are no reference to the year at all (I believe).........
On numbers with reference to the year, the next two didgits refer to the week of that year - the rest are the number within that week.