Dr.RaviCardio said:

They are two different exemptions from the same federal requirements and they buy different things.

This is where I part company with the consensus forming above. 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.

AussieAnna said:

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

Compounding pharmacy response time test for compounded supply: I email customer service at odd hours to test responsiveness. A pharmacy that can't answer questions promptly is a red flag.

My current pharmacy: average response time 4 hours. They answered my questions about reconstitution thoroughly and professionally.

Communication quality is a proxy for operational quality. A pharmacy that communicates well is likely manufacturing well too.

Dr.AddMedPHL said:

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

Price comparison for compounded supply across sources I've used:

I use the 503B option — best balance of quality, cost, and legality. The brand price is insane but insurance can help if you qualify.

A narrower follow-up, since the general answer is now clear:

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

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.