Obviously barring material changes, HT/ST angles, specs for tyres and fork capability etc, main structural changes are:
1 =bolt on disc brake adaptor, horiz DO, V brake bosses, 26.8 or 27.3 SP. (US made)
2 = same but 27.2 SP + (other differences?!)
3= dropped V brake mounts, HT gusset, 30.9 SP, replaceable Der hanger
4 = (big changes to frame design/angles over classic models) vertical DO, EBB, no V bosses. Last models dropped the square chainstays IIRC.
5 = eekk, WTF.
Not sure if it applies to later models but early US (mine) has the
last two EDIT - first two digits as year.
Still, absolutely loving mine - posted a while back on here, link below - set-up different now but still going very strong:
viewtopic.php?p=195619#p195619