Ammo, whist not supporting your expressions of "No good" and "Failed" for unsuccessful TT riders, (and note that I have never had the guts or means to be a road racer), I believe that the matter is up to the organisers in conjunction with riders representatives.
Look how both the MGP (formerly the Amateur TT) and the TT itself have developed over the years.
I would expect that most of the "Unsuccessful" TT riders will be of "Amateur" status anyway.
What ever the outcome, to a mere mortal such as me, all MGP and TT riders (and passengers) are still heros.