This is something of an indirect answer, but the "National Waiting List" letter your son received from WP is likely a "3Q" letter. It's something of a misnomer that it includes the NWL verbiage because it can mislead applicants into thinking that they lost their MOC slate and are down to waiting on the NWL for a spot . . . which is NOT what it actually means. Any number of WP applicants have posted that they received one of these, only to be followed within a couple weeks by an appointment.
Anyway, as for your question, I don't believe Annapolis sends out 3Q letters. I don't know, however, whether they otherwise inform applicants that they are on an NWL at any point in the process.