I wonder how the rules and format of the year-end championship in the ATP tour and WTA tour evolved.
For example I notice that in 1985 men played knock-out tournament, whereas in 1986 the semifinalist were decided in round-robin. I see a similar change between 2002 and 2003 women tournament. The first men's masters tournament in 1970 involved only 6 players playing round-robin. In 1984-1998 women played best-of-five, while in other editions they played best-of-three.
What were the changes of the format of this competition in the past? (How did the number of contestant change? Which tournaments included round robin? In which editions only round-robin/only knock-out tournament?)
NOTE: I see that for men's this is basically answered by the Wikipedia article I am linking to. (Well, unless there were some other changes of rules which are not mentioned on Wikipedia.) I quote from the current revision of the article
Eight players are divided into two groups of four and play three round-robin matches each against the other players in their group. The two players with the best records in each group progress to the semifinals, with the winners meeting in the final to determine the champion.
The current round robin format of two groups of four players progressing to a semifinal and final, has been in place for all editions of the tournament except the following years:
1970, 1971 - Round robin with no semifinals or finals, winner decided on best performed player
1982, 1983, 1984 - 12 player knock-out tournament with no round robin. The top four seeds in the event received a bye in the first round.
1985 - 16 player knock-out tournament with no round robin
However in the current revision of the Wikipedia article about women's finals I see only this short mention about the format of the tournament:
The month, city and number of players has changed since the first edition in 1972. Since 2003 there have been eight singles players divided into two round robin groups, and four doubles teams.
It does not say how the format/number of players changed before 2003
