DS had enough AP credit to be considered a “sophomore” his freshman year. Each year he got emails as if he was a year ahead of himself (ie offered to register for classes as a junior when he was a sophomore, got info on buying his senior college ring when he was a junior, etc). IIRC, he still took the sciences college courses (that he’d taken APs in) but used some of his AP credits to satisfy distribution requirements and/or to meet prerequisite requirements so he could take a higher level class.
As for HS, most schools around here (public and private) require students taking AP classes to take the AP exam. IIRC the student acknowledges it when they register for the class.