I am a bit thick, so bere with me, but how did the frame on the prototype frame you have pictured, differ from the others..?
1. Simplex dropouts vs. machined ones (like on later FRO, ARC, Ulitmate)
2. Cable stops on top tube are bonded onto the carbon section, later C-26s had cable stops welded onto the metal sections of the frame
3. No reinforcing gusset on the drive side chain stay like later FROs
4. Cable stop actuated front derailleur as opposed to using a pulley to route the cable to the front derailleur
1. The prototype bike had a custom made FTW stem that was a sort of forerunner of the modern day threadless type stems. An extension tube is brazed onto the Yeti fork and the stem clamps onto that extension like today's stem. Fork is still threaded and uses a threaded headset.
2. Decals didn't say C-26, just Yeti, Shimano, Easton and so on in different photos
So the tubes used for the prototype build were the same as the Race frames that where built,...........?