On the subject in the title: Revisiting: US compounding rules and how they changed Working notes rather than a conclusion.
Regional question, dated February 2026, because everything in this category expires.
The position differs between the jurisdictions people usually treat as one, and the differences are not marginal. I have set out what I can verify for my own region from primary sources rather than summaries.
If you can confirm or contradict this for yours, please date the answer.