Dolly Mixture from 1973 is the earliest dated film of Marks that was known to have been shot in both hard and softcore versions (the hard version was made first, the soft version a week later), while in 1979 he made a film with Nicky Stanton that was shot in a soft version (that Marks put his name to) called Busty Ravers, and a hard version (that Marks didn’t put his name to) called Busty Baller. So it seems fair to assume he was anonymously shooting h/c for most of the 70s.
Heres an Ad for some soft core Marks from late 1970
