Look
The numbering was component choice, the frames had the tubes mitred i.e. cut in to the joining tube then slotted in, welded then internally, then reamed where needed, head tube, BB shell etc, they were hand built, but were not that light as back then racing was a 3 event affair, hillclimb, downhill and XC, all performed on the same scrutineered bike, so they had to stand the hammer of World cup downhill courses. which were of course not as extreme as now, but still rough.