The Buescher company, and most of the other big manufactors, started to laquer saxes in the mid or late 20's but during the "roaring decade" silverplated instrumnets was most in demand. After 1930 (gold)laquer saxes was standard at the Buescher company and (silver)plated saxes was just on special orders. Buescher discountined the TT's to -34-35. After that the TT's became stencils.
Thanks Thomas, for the interesting background info.
So my TT, from 1927/8 may originally have been bare brass but equally could have been factory laquerred, or may have been returned for laquerring at a later date, as Pete suggests. Either way, I think it's going to come off soon.