I just double checked: R was used in Australia to mean restricted until around the 80s.
From 1970 it was G, NRC, M and R. This became G, PG, M, R18+, then X got added in 80s, then MA15+ in 1993. That explains why Predator 2 was rated R18+ and ALIEN 3 M15+ despite neither of those ratings being appropriate - they were too early for MA, which they both are.
Actually explains a lot of older movies being R18+, AND why every vhs in the early to mid 90s had that ad explaining the rating system on it...