Dr.SportsMedIN said:

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

I read this differently from Dr.SportsMedIN, 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.

lucas_SP_BR said:

My pharmacy stopped supplying with three weeks notice and a letter that explained nothing, so I went and read the statute.

Beyond-use dating (BUD) for compounded supply compounded products:

Lyophilized (unreconstituted): typically 6 months from compounding date
Reconstituted with BAC water: typically 28-30 days refrigerated
Reconstituted with sterile water: typically 24 hours (no preservative!)

Always use BAC water for multi-dose vials. Sterile water has no preservative and supports bacterial growth after first puncture. This is a common and potentially dangerous mistake.

Dr.PeteFamMed said:

A research-chemical supplier selling lyophilised powder labelled research use only is not compounding and is not claiming to.

Compounded semaglutide formulations for compounded supply: some pharmacies add ingredients like B12, L-carnitine, or BPC-157 to their semaglutide preparations. Are these beneficial or marketing gimmicks?

My take: B12 addition has some logic (GLP-1s can deplete B12). L-carnitine evidence is weak. BPC-157 for GI protection is theoretically interesting but unproven. I prefer straight semaglutide with no additives — fewer variables, cleaner data on what's working.

Following on from LondonLisa — and this may be the naive question:

What actually distinguishes 503A from 503B, in terms of what each may make and from what starting material?

Reporting back.

The bulks-list asymmetry was the piece I had missed entirely. It explains why one of my two pharmacies is still arguing it can supply and the other simply stopped.