I was an employee of the U.S. Yamaha plant. I was a sax assembler and tester. I never seen any serial numbers that matched any type of pattern, and as far as I could see, there is no way of actually knowing the exact production date. However, the very day the sax is finished it was packed into the shipping box and tagged with a printed sticker. On that sticker I believe is the date it was packed. When a specific quantity for a specific order was built, then they were shipped to the customer. That would be the recorded shipping date. But, I seen it take two days before, for the saxophones that were finished to be packed. So there were many irregularities with the serial number and exact assembly date. Yamaha, to the best of my knowledge, never used serial numbers to be a record of the day they were built. I wouldn't think that any other company could give you an exact build day just by the serial number. Yamaha would have all there parts built in Japan and Indonesia (and in the past three years it was exclusively Indonesia) and then pack and ship those parts to the U.S. Then the bells and bodies were buffed and lacquered in the U.S. factory. They were then assembled and adjusted and tested. So from the time the bell was being hammered out, and the body tube was formed (which then had the serial number stamped in) it could be months before it was shipped to the U.S. to be built. I'm not sure if I got off a bit with my reply, but I hope this info helps out.