A given papal letter may, or may not, refer to an infallable doctrine. Ordination Sacerdotalis, it has been confirmed, did.
We must recall that the Deposit of the Faith cannot be added to or subtracted from. Most authoritative pronouncement in history have been made to confirm that something is part of the Deposit of the Faith when it has been denied or disputed. A pronouncement does not add to the Deposit of the Faith; it points to something that has always been there.
Blessings,
Gerry
