Doubtful on actually reaching a cap, more likely that a combination of factors will result in not requesting a waiver or not granting one.
It is most likely that a waiver won't be requested because you really aren't competitive (ie, there is a likely vacancy winner who is qualified already), or it is so late in the process that they cannot process it in time to set the class. It is a simple way to narrow the pool down without having to use resources to ultimately send Qualified Non-Select letters. As with anything in admissions, get everything done early, and you benefit on both counts. It is a lot less likely in October that West Point will have in nominations, fall test scores, and completed applications to predict who is going to win a particular vacancy meaning they will usually request a waiver over a greater distribution of candidates. The 90-day average to fully work a medical waiver wouldn't even touch the file completion deadline at this point, let alone the medical qualification deadline usually set as mid-April (compare that to someone who waits to finish in February and needs a waiver - on average, it would be done at the end of May when all the spots are full).
None of these are absolutes as there is not a rule that says if complete by X date, request a medical waiver. A lot is subject to that RC and ultimately the director of admissions. That variances increases with another couple unknowns - is there something in your file that makes them not want to request a medical waiver because they would also need a waiver for something else, or you have a condition that they know a waiver cannot be granted for.
Once a waiver is requested, there is no guarantee that the USMA Surgeon will recommend approval or the committee will confirm that recommendation. The average is 90 days, but some of that depends on how quickly a candidate navigates the waiver process submitting required further documentation and test results. If you want that waiver to go through, you have to be responsive/proactive in getting all the requests done.
