First use the cosmetic features to get a range of possible years.
Next, (if applicable) look for the date code on the tube chart.
I believe all my Silverface amps have no two-letter date codes. Both have SN's that start with F3xxxxx and was told that meant 1983.I have Paul Rivera era amps and Bruce Zinky Amps to check. I could be wrong, but I've nothing to counter that comment for accuracy.Stock Speakers Outside the chassis, Fender has used several different speakers in some Blues Junior models.All green boards and all black Tolex BJrs use the Fender Special Design, which is built by Eminence and is equivalent to the Eminence Legend 125.Such as N for nineties, E for Eighties, S for seventies, etc?
Or, are we talking about the build date of "HJ" etc? Toppscore Guitars have a year code within the serial number as you've indicated, amplifiers do not.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.It’s a little weak in the bass and the highs are a bit more muted than the other speakers. Look for a sticker inside the cabinet like the one in the pic below, or similar sticker on newer amps.If your amp dosen’t have a date code, flip the amp upside-down and check the transformers, and speakers for their manufacturer codes.