Until the scions are completely brown and dead: don't give up! I grafted buds at the wrong time of year (august) and they sat there for 6 months until the right time came along and then started doing their thing. Won't do that again... Even if the scion dies, don't stop, just wait for the rootstock to come back and graft something new the next year :-). I'm sure you can tell I have experience with that, ooops.
So, can one rate the graft quality by the number of rootstock buds that sprout? E.g., a one-sprout graft is better than a three-sprout graft? Hmmm, I guess the number of available buds, i.e., grafting height, must play a role too?