It sounds like you are describing Tectum deck. The company that produces Tectum is still in business - you should be able to get load tables from them.
If you are using bulb tees, then the system is a cast-in-place gypsum roof deck. The board on the bottom came in two forms...gypsum board and fiberboard. Both were just forms for the gypsum material.
Not necessarily, Ron. It could be Tectum or Insulrock. Since he called it "fiberdeck", that would be my guess. We used a lot of Tectum on bulb tees in the 70's.
hokie66...I saw a lot of Tectum in the 70's and did a lot of load testing on one of their competitor's products (CPI), but it was mostly on OWSJ. Certainly amenable to bulb tee applications, though.