I think the Virginia Slims (briefly Avon) championship was considered the third part of a triple crown - W, USO, VS. After that the Colgate year end championships which didnít debut until fall 1976 followed by the Family Circle Cup in the spring. This roughly covers the time period from 1973 to 1979. When world team tennis disbanded at the end of 1978 the French and leading clay events had many more top name entrants in spring 1979. Austin beat Evert in the semis of the Italian that year over a field which included Goolagong, Wade and a few others. The Australian lagged a bit and didn't get top players until 1980 (Navratilova, Goolagong, Mandlikova, Turnbull). It basically joined the others as a top notch field in 1981 when Evert finally appeared nearly 8 years (!!) after her first and only appearance and Austin made her one and only appearance, never to go down under again. Evert didnít play 1983 and that lessened itís luster a bit, but by 1984 each and every slam had all the top players from that moment on. At certain points in the 70s it only seemed the Aussie or French were important if Margaret Court was winning a true slam (1970) or Bjorn Borg was chasing one with the first two titles under his belt, 1978-80. Jimmy Connors famously stated he would follow Bjorn to the ends of the earth (Oz) but only if BB won the third leg at flushing. Sadly he never did and the Aussie was always robbed of many top male players until roughly 1988.
Thank you for your explanation Mark! It was very thorough.
So basically, if I understand well, we could say the most important events were, according to the period:
1968-1971: Wimbledon, US Open
1972-1976: Wimbledon, US Open, VS Championships
1977-1978: Wimbledon, US Open, Avon Championships, Colgate Championships
1979-1980: French Open, Wimbledon, US Open, Avon Championships, Colgate Championships (was one of these Masters more important than the other?)
1981-Today: Australian Open, French Open, Wimbledon, US Open, VS Championships (now WTA Finals), Toyota Champs (in 81 and 82)
I'm not quite sure if the FO was a truly important event from 1972-1973 though. In 1972 you had a field with BJK, Goolagong and Casals. In 1973 you could add Court and Chrissie in there (no BJK though). That kind of implies it was big back then.
In fact, from the beginning of the open era, it seems it had pretty good draws up until 1974. So maybe the FO could be considered a big title on par with Wimbledon and the USO for the 1968-1973 period?
One could make a case for the AO too, at least for the years BJK played in 68 and 69.
PS: I agree it's a shame about Borg. If he had won the USO, he would have travelled to Australia and thus save the AO (which went through a BIG crisis on the men's side during that period, I think they didn't even get the top players till 1984, a few years after Evert and Navratilova played it again).