Obviously, I don't know the details of 1970s/1980s plasma products, but I think it's probably fair to assume that they were screening for pathogens they knew about at the time. I think in retrospect it's easy to say that they should have taken the factors off the market sooner, but at the time it was probably a very difficult situation. Hemophilia is an incredibly dangerous condition without treatment and there was a reasonable expectation that people would die without access to clotting factors.