Composite constraints (like "Person" or "Taxon Name") could be lost during migration from templates to statements on properties. One possible solution could be to let the user enter "Person" as value of the Constraint-Statement and in the background the four constraint statements get created via an API call.
As far as I know there were 2 type of constraints on the talk pages: the regular constraints, which now are converted to statements and the complex constraints, which never were linked to Quality Constraints and the reports are maintained by PLBot. Other constraints I've never spotted on talk pages. If @Jonas.keutel isn't talking about complex constraints, I suggest he adds links to property talk pages that have composite constraints.
I see, thank you… but that template was subst only before this issue was even opened, so if I understand correctly there’d be no difference between composite constraints and regular ones except when you added them.