I think the first year (maybe the 2nd as well) was the only year they came stock with a leather covering, after that it still remained an option as it does today with all the current amps.
As far as the serial number, I don't know how to tell that? But if your amp has only a single knob to share for the FX loop on the back then it's a '94 and it's a serial loop ...........unlike the later models starting later that year until the end of production that had a knob for the send and a knob for the return which is a parallel loop.
Thats my $.02 worth...... well, actually about $.01 :wink: