RC31s were essentially all the same, only the decals changed to match the other forks in any particular years production until the colour change. I think there were 2 different lengths initially, increasing to 3 later[I will try and check]
The nasty 'retaining screw' in the back of the legs was dropped after the first production runs.
The only other changes were the move to the smooth lacquer on the carbons and the introduction of the Ti Rc31 which had the leg spigots in ti as against steel.
The crowns and dropouts changed to match the RC39 crown in the charcoal colour in later production, I will try and work out when that happened.
There was of course the short run of RC29 rigid forks with longer carbons to suit 29ers.