At some point, I was told that non-BCS teams cannot rise above A-. Unfortunately, I do not remember where that info came from.
One thing to keep in mind about the way prestige is done, it only takes one bad season for someone like Montana to see a lot of their gains slip away as the pull of the baseline is like an anchor. That to me is the greater flaw of the system.
As far as a NC? A NC 5 seasons ago means ZERO in the current system. Again, a huge flaw.