Bryston serial codes-how do you get date?

Know I got an email fom a prspective seller but unfotuntely didn't write it down nefore the email got deleted.If amybody can help me out be apprecited.Was really looking for an 4B ST but fellow who gave me info was early in bidding on Ebay with a B60 and I think it had not only the serial code but also adate code stickermaking it a snap.I am getting impressionm that folks are spending same amount on Brystons that is 16 years old verus one that is 4 years old which any small updated to cicutry before new series seesm to not make sense just because well one if practically new the other is at the end of many amps life spans.Not sure if the ST's will last 25,35.or 50 years (certainly they are better built since 20 years when it comes to amps is end of life of the average Bear.But want to know what I am looking at if serial is given.Checked Bryston site and it wasn't much help beyond touting 20 years.
Much thanks
Chazzbo