Drywood -
I remember several years ago an experienced collector (not active now) told me he had the Bear serial numbers all figured out and could tell me the year of the bow just by the serial number.
I offered to have him come to my house and identify 10 Bear bows, just by the serial number and to bring $10,000 cash with him. For every bow he could date accurately from the serial number, I would give him $1,000 cash, and likewise for every bow he identified incorrectly, he would give me $1,000 cash.
He declined my offer using the excuse that he lived several hundred miles from me. I offered to send a taxi for him, because I knew his chances of correctly dating any of the bear bows was almost zero. He still declined, knowing he would never be able to identify the bows I selected. Simple put, there are lots of exceptions to most rules for using serial numbers to identify Bear bows.
For fun I gave him a couple of numbers for free. He missed both badly and was 10 years off on one.
If I remember correctly, at one point I identified 14 changes in Bear's serial number methodology. With all the changes and exceptions, the serial numbers are not 100% reliable.