An RAE cannot be directly converted into an IU without knowing the source(s) of vitamin A. For example, the RDA of 900 mcg RAE for adolescent and adult men is equivalent to 3,000 IU if the food or supplement source is preformed vitamin A (retinol).
On the other hand, an Associate degree is a title conferred on a student when he completes a college study. Diploma is usually given in vocational or professional courses, like designing, pharmacy and engineering. High schools, trade colleges and professional schools confer Diploma certificates.
I cant tell you much about diplomas as I am a B.tech myself. But the main difference between a post graduate diploma and an advanced diploma is that a post graduate diploma as the name suggests is a PG diploma, whereas advance diploma is same as the regular diploma only that its a 3- year degree course as compared to a 2-year regular diploma.