One concrete data point for the thread. Two things anyone can check: a state licence number for a 503A, and an FDA outsourcing-facility registration for a 503B. Both are publicly searchable, and a pharmacy unwilling to give you either has answered the question.

One thing that is still open after Dr.EndoIndy’s answer:

Why a shortage listing created a legal pathway at all, since a shortage is a supply fact rather than a permission?

raj_cambridge said:

Two things anyone can check: a state licence number for a 503A, and an FDA outsourcing-facility registration for a 503B.

Coming at raj_cambridge’s question from a different direction. The shortage clause is the answer to the second question and it is a subtraction rather than an addition. Both exemptions forbid compounding something that is essentially a copy of a commercially available approved product. A product FDA has listed as in shortage is not treated as commercially available, so listing removed the objection that otherwise blocked compounding. It never created a permission; it withdrew a prohibition, which is why it evaporated the moment the supply fact changed.

Reporting back.

Follow-up — I binned the frozen one. Aggregation does not undo itself and I was not going to inject a maybe.

CarlaRPh_TPA said:

The shortage clause is the answer to the second question and it is a subtraction rather than an addition.

That is correct as far as it goes, and here is where it stops going. Worth adding the genuine exception, because it is real and narrow: a change made for an identified patient where the prescriber determines it produces a significant clinical difference for that patient. A grid of fixed doses offered to everybody is not that, whatever the intake form says.

Worth separating that from compounded supply, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.