JakeBK_lifts said:

Resolution therefore closed the doors unevenly, and the asymmetry follows from the bulks lists.

No disagreement with JakeBK_lifts. One condition attached. 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.

JakeBK_lifts said:

Resolution therefore closed the doors unevenly, and the asymmetry follows from the bulks lists.

I read this differently from JakeBK_lifts, on substance rather than tone. A research-chemical supplier selling lyophilised powder labelled research use only is not compounding and is not claiming to. It is a different legal universe with no pharmacy oversight, no patient relationship and no content guarantee, and conflating the two in these threads helps nobody.

I would rather be corrected than agreed with, if it comes to it.

This one has a reasonably settled answer, so here it is. They are two different exemptions from the same federal requirements and they buy different things. A 503A pharmacy is regulated primarily by the state board, needs a patient-specific prescription, is exempt from CGMP, and may use a bulk substance that has a USP monograph, is a component of an approved drug, or appears on the 503A bulks list — three independent doorways. A 503B outsourcing facility registers with the FDA, is inspected on a risk basis, must comply with CGMP, may compound for office stock without a patient-specific prescription, and has one doorway to a permitted bulk substance: the 503B bulks list, or the drug shortage list.

PharmacoVig_BOS said:

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

Can confirm. Same sequence, different timescale.