My understanding is that the official rule on SNAs that have already cleared is that the SNA is returned only if you cancel the entire reservation and you must do this by 3 pm on the day before arrival (where 2 pm the day before arrival is the final sweep for the SNA upgrade to be confirmed). I'm not sure if it matters whether one is already beyond the cancellation deadline for the underlying hotel reservation, but since 3 pm the day before arrival would be beyond the standard 48 or 72 hour cancel period that most hotels impose on standard reservations, I wouldn't expect a stronger rule requiring forfeiture of the SNAs too.