First I would like to thank everyone who responded to our request for data as outlined in the initial article that was printed in March 1997 issue of TCG.
Most notably, I'd like to thank Jeff Lacio for his contributions to our research.
New panels made after the CBS acquisition were used beginning in April 1965 and say "Fender Musical Instruments." So, if you have January 1965 amp, it will have a Fender Electric Instruments panel whereas a January 1966 amp (even though it has that green "OA" date stamp) will have Fender Musical Instruments. Although the database doesn't have thousands upon thousands of entries, we are seeing some interesting patterns emerging that will help date amps by serial number. The early amps (woodie and tweed) had serial numbers handwritten on the tube chart.
These appear to be used sequentially independent of model.
After reading Teagle and Sprung's excellent Fender amp book, I took them up on their challenge that maybe someday someone will compile enough serial numbers so that Fender amps can be dated that way. I contacted several Fenders collectors and dealers who were kind enough to supply me with data.The biggest tip off would be the control panels which brings us to interesting factoid #2.