2006 amps have a small metal “Fender 60th Anniversary” button on the back plate. Early Tweeds The early green board tweed-covered amps were not lacquered. It has the same cream board inside with the same components as every other current-production Blues Junior.
The serial numbers for these amps begin with “LO,” indicating that they were made in the Fender/Sunn Lake Oswego factory. It usually applies to old vacuum tubes/valves that have gone unsold for decades. All cream board tweed Blues Juniors have a “Limited Edition” plaque on the back.
Unlike the auto industry which has specific model years for their products, most specifications for a given Fender instrument model, change little if any, through the lifetime of the model.
While there have been periods where dramatic changes have occurred, for example: the transition periods between Leo's Fender and the CBS years, as well as the transition between CBS' Fender and the current ownership, generally speaking, most models are feature specific and do not change from year to year..
Serial numbers have been used in various locations on Fender instruments through the years.
All green board and all cream board Blues Juniors are identical electronically, despite what the salesman told you. Below is a table of revision dates and the changes made on those dates. Fender adopted a two-letter dating code in 1990, and the code can be found on the Quality Assurance label, inside the cabinet, sometimes located on the bottom, next to the reverb tank, sometimes on the side.
The codes are usually handwritten, and the letters can occasionally be hard to decipher. There is no reliable way to date 2003-2005 amps other than to ask Fender customer support to look up the date from the serial number, although you may find a date code on the speaker.