I thought I understood embryo grading

Elisa • Married 2ectopics, 1 ovary. First FET 2/13/19-BFN Second FET 4/3/19-BFP Boy/Girl Twins

Or am I confused. I’ve seen people say they had perfect embryos that were 2AA and then perfect 6AA. Should I just forget the number and consider that AA embryos are good no matter the first number?