The S-225 was still being developed well beyond 1972. It was cancelled no earlier than 1978 according to everything I've seen so far. It was a massively secret project due to the ABM Treaty restrictions and that is why you heard absolutely nothing about it until well after the Cold War ended.

Here's a pretty decent broad overview of Soviet ABM history:

http://www.fas.org/spp/starwars/program/soviet/990600-bmd-rus.htm