Basically this only means more money to earn for a soundtrack/library composer, and considering the huge amounts of movies shot during the 70s, it seems almost natural that some composers could use their music again for another movie.
It'd be actually very interesting to draw a whole map of these soundtracks and their use.
This is really more and more hard to do for libraries and sonorization records: I've tons of these records and I completely ignore which TV programs, documentaries, etc., they were created/used for.