1: Retroactive is not proactive. It is punitive. (Even an academic should be able to wrap his brain around that one.)
2: Applying a standard, retroactively, especially one that impacts one and only one school (for practical purposes) is "capricious", and as there is $ involved, it is also actionable under tort law.
3: Attempting to apply such a standard would, undoubtedly, result in a lawsuit and the discovery process would be....eye opening.... as the variations among the reporting institutions methodologies would make the APR number, itself, arbitrary.
The resulting lawsuit is a great big LOSER for the NCAA and even an academic should be able to wrap his brain around that. And, if not, then it is very likely that his attorney will be able to spell it out for him....in that dollars and cents kind of way that only an attorney can spell out such things....
Finally: As people have already discussed, this whole thing is a cluster fuc&, already....the NCAA needs to standardize its reporting methods, before it does another damned thing on this issue....then it needs to improve its auditing of the reporting.
Once that is in place, it can derive the appropriate "mandatory compliance level".
Once those things are in place, you start the "compliance clock" and give the institutions their "three years or else" (or whatever timeframe it is) mandate.
Absent the establishment of this groundwork, they would punishing (only some) institutions for "normal" behaviors.....and they will be, correspondingly, losing expensive and embarrassing lawsuits, as a direct result.