Before that,it was non-A non-B hepatitis.
It's only an STD under rare circumstances. In 1972 they knew there was another viral hepatitis out there, but they did not perform diagnostic tests to determine which hepatitis a patient was infected with. They just didn't have the screening tests developed at that point. HCV was not clearly identified until 89 or 90.
1992 they found it after I was diagnosed after years with chronic hepatitis.
That was the year they started testing for it.
An interesting paper from 2004 discussing what had been learned in 15 years (i.e. HCV started being recognized as that in 1989 as per Andiamo above)
Paper also includes speculations - by 'reverse genetic engineering' - of human co-existence with the virus for the last 100,000 years.
Another paper discussing the 'patent dispute' over the virus between Dr. D.W. Bradley, who had been working with nonA/nonB virus since the 1970s, and Chiron corporation. This paper is a good starting point for understanding why everything related to HCV is so expensive.
Although it wasn't named until around 1989, its believed many Vietnam Vets got it from the shots given in those days.