cas, that isn't exactly true. USNA can accept as many enlisted that have a nomination. The SECNAV can nominate 85 Regular and an additional 85 Reserve USN/USMC personnel. Because NAPSTERs have to join the Reserves, normally all of those 85 will go to NAPSTERS (minus the enlisted that are on active duty/regular). There were 67 prior enlisted that entered USNA (including those from NAPS) and all of those likely were active duty/regular. Presuming that all 85 SECNAV nominations were used for the active duty enlisted (and this may not all be true), that means that 18 nominations were not used/needed (meaning all active duty applicants were appointed) or were used and those individuals were not selected for appointment (meaning they weren't qualified).
I have not seen a cap to the prior enlisted quota beyond what the SECNAV can nominate. A prior enlisted individual has all 4 other nomination categories still available (3 MOCs + VP).