I am very confused here. AP credits have absolutely no bearing whatsoever on applications to graduate school. Whatever AP Research entails, it’s not going to be moving the needle for PhD programs. Further, whether someone got academic credit for their research or not is also irrelevant. If it’s something you’ve done in your past, it goes on your CV/resume and in the appropriate fields of the application, and gets considered by and admissions committee whether it was for credit or not.