To draft a QB every year you have to keep 3 QBs on the roster. For example if we had been using this model right along we would have the current starter, current back up, last years draftee on our roster right now. We draft a QB in a round where ever there is good value. In training camp the coaches "should" know by now if the back up is going to supplant the current starter. He has been in the system for 2 years now. If he does the starter moves to the back up. Whomever the back up is now is in competition with last year's rookie. If Last year's rookie is better the back up is let go. If the back up is better then last year's rookie must be better the this year's rookie or he is gone.
Coaches should be able to tell pretty quickly if a QB has something. I mean Rex was saying pretty early in camp that Tyrod had a good chance to win the starting job.