DataDave said:

The dose-response is real but shallow at the top.

I read this differently from DataDave, on substance rather than tone. The trial means are being read too generously in this thread. STEP populations were selected, supported, and titrated by protocol, and the real-world curves are consistently a few points worse. That difference is not noise, it is what happens when you remove the study infrastructure.

Adding the numbers, since they settle part of this. Worth knowing that the injection site changes very little. Abdomen, thigh and upper arm are bioequivalent for semaglutide, so a site change is not a plausible explanation for a bad week.

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

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

DebRD_ATL said:

The trial means are being read too generously in this thread.

There is a second half to this that has not been said yet. 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.

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

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

Closing the loop on my own question.

Six weeks on from posting: I stopped reading the weekly number and started reading a four-week average, and the "stall" I opened this thread about was a 1.8kg loss I could not see.