Compulsories usually only had two tumbling passes, but even in the 70s, almost every elite gymnast was doing three tumbling passes (Nadia, for example). As the base score without bonus was lowered in elite gymnastics, gymnasts needed to do more tumbling to get that bonus, and I think the tipping point was after the 1992 Olympics starting with the 1993-96 code of points. There's quite a big difference between starting from a 9.4 (college) and starting from a 8.8 (00-04 Code of Points). College gymnasts can get away with saving their body by doing only two passes because they have more difficult leaps and jumps in their repertoire than they did in the past, but most college gymnasts used to do three passes before the open-ended code in elite gymnastics, which encourage a high level of difficulty in both tumbling and dance elements. The last three Olympic floor champions (Podkopayeva, Zamolodchikova, Ponor) under 10.0 all did four passes, and it was very common beyond them. By 2000, it was pretty rare to see someone only do three passes, like Svetlana Khorkina or Elise Ray, but they could rack up difficulty with their dance elements.