Following on from Dr.LeslieOBGYN — 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?

lucas_SP_BR said:

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

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. I would resist the confidence. Half of what this board was certain about two years ago has since been quietly dropped, and nobody went back to correct the threads.

lucas_SP_BR said:

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

No disagreement, though the timescale matters more than the mechanism here. Most of what looks like a difference in kind turns out to be a difference in how long somebody waited.

lucas_SP_BR said:

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

That reframing is the part I needed. Sending this to two other people who asked me the same thing last week.

Adding the clinical framing, because it changes how the question reads. Take it one variable at a time. Almost every unanswerable question in these threads is unanswerable because three things changed in the same fortnight, and no amount of subsequent argument can untangle them after the fact.