SkepticalSean said:

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

Compounding pharmacy licensing verification for compounded supply: before ordering, verify your pharmacy's credentials:

1. State Board of Pharmacy license — check on your state BOP website
2. FDA registration (for 503B) — check on fda.gov
3. DEA registration if handling controlled substances
4. PCAB accreditation — voluntary but demonstrates commitment to quality
5. USP <797>/<800> compliance for sterile compounding

This takes 10 minutes of research and could save you from receiving substandard or unsafe medication.

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?

josh_phd_bmore said:

Compounding pharmacy licensing verification for compounded supply: before ordering, verify your pharmacy's credentials: State Board of Pharmacy…

FDA inspection results for compounding pharmacies selling compounded supply: you can look up any 503B facility's FDA inspection history on the FDA website.

Check for: Form 483 observations (violations), warning letters, and recall history. A clean inspection record is a strong indicator of quality. My pharmacy has had 0 Form 483 observations in their last 3 inspections.

This is public information. Use it. Link: fda.gov/inspections-compliance-enforcement-and-criminal-investigations

Closing the loop on my own question.

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.

BariatricNurseD said:

FDA inspection results for compounding pharmacies selling compounded supply: you can look up any 503B facility's FDA inspection history on the FDA…

Agreed, and the enforcement dates were staggered by category — 503A first, 503B a few weeks later — because outsourcing facilities have manufactured inventory and clinic contracts to unwind while a 503A makes to order.