I've just done an internet trawl and cant find anything about XTR thumbies......
Even Google comes up with 'did you mean to search for XT thumb shifters'.
Were they a differant design to XT or DX thumbies? How did they differ?
What would they have done to warrant an XTR version? Not much technology to throw at a thumbie, lighten the action and it becomes too easy to overshift so maybe just throw a bit of Ti at them :?
If they do exist i can certainly see why Shimano never comercialised them.
gotta say folks, if a few pros back in the day wanted to carry on using thumbies, would it not have made sense for them to strip the black ano off XT's polish em up a bit....etc..Maybe the factory did a few sets in silver to blend in with the New shiny M-900 XTR? First Flight bikes may know! Or maybe a quick e-mail to Richard Cunningham at MBA may resolve this
There where a small converter which let you mount XT thumbshifters on the XTR breake lever. Maybe that is what you saw. Dont think it was a proto, they usually dont put stickers on protos. 101 % sure it was homemade sticker.