Can't say as I've ever looked for a frame number, and the only stickers are the Reynolds tubing ones, and a little bike shop sticker at the top of the downtube, of the bike shop / guy I bought it from. I bought it from a bike shop closing down sale because I'd always wanted a 531 frame, and up to that point never had one, and although it was a bit of a gate for me, I was only really going to build it up as a road hack bike - which I did and used it for a year, until I bought another frame, and used most of the parts on that.
I suspect there were various flavours of Reynolds framed framesets, unbranded, with similar design / build, sold by some bike shops that kind of brand their own frames. At the time of buying it (95 / 96) it was all a bit slack angled, almost horizontal rear dropouts, and almost road / touring feel to it (thinking about things like the cable guides and stops. Flick / ping testing the tubes, shows a reasonable degree of butting, but it's probably a bit lardy compared to mid 90s, mid-range steel MTB frames.
I've kept it for posterity, and the hope that when I've got more time, I can tidy it up a bit, and build it up again. That might be more than ambitious at the moment. It's a shame I haven't any pics of it built up - it was built to a price point, because I bought a STX / STX/RC groupset, and a pair of Mavic 230 rims - but in the mid 90s, taking photos wasn't quite as pervasive as it is these days, plus it really was only a hack / commuter bike.
