You got me interested, Rollo.
I looked for each month's all time great and come with this:
: Darlene Hard (Jan 6). By far the hardest month to find among the greats. But I know Kerber comes here as well since she shares my birthday (18).
: Mandlikova (19). Second rarest month to find among the greats. Mandlikova is the only one born this month among the greats who won more than 2 slams.
: Molla Mallory (6) comes first. Then Brough and Osborne (4 and 11). Also Bessie Moore (5), Hilde Sperling (26) and Jennifer Capriati (29).
: Maria Sharapova (19) takes it. Followed with Daphné Akhurst (22) Angela Mortimer (21) and Juliette Atkinson (15).
: third rarest month among the greats (above 2 slam winners at least). That's for Suzanne Lenglen (24).
: a big month to become a champion. Steffi Graf owns it (14). Followed with Venus Williams (17), Justine Henin (1st), Doris Hart (20), Kim Clijsters (8), Shirley Fry (30), Lindsay Davenport (8, same as Kim), Mary Browne (3) and Joan Hartigan (6).
: the one and only, Margaret Court (16). Also Evonne Goolagong (31), Virginia Wade (10) and Dorothy Round (13).
: Helen Jacobs, Pauline Betz and Althea Gibson share it! All 5 slams winners. Jacobs and Betz also shared the same birthday, August 6th. Althea was born August 25th.
: by far the biggest month to become an all-time great! Even intriguing to notice a streak of pairs: 22, 24, 26, 28 and 30 september. Serena Williams takes it indeed (26). Followed with, but not the least: Maureen Connolly (17), Dorothea Lambert Chambers (3), Martina Hingis (30), Alice Marble (28), Lottie Dod (24) and Charlotte Cooper (22), all 5 slams winners or more.
: Helen Wills (6) takes it to Martina Navratilova (18)! 19 slams to 18 slams, excusez du peu.
Maria Bueno (11) comes third, Ann Haydon Jones fourth (7).
: Billie Jean King (22)!
Then Blanche Bingley Hillyard (3), who also did much for womens tennis in the pioneering years! One hell of a constructive month.
: Chris Evert (21). The Queen. Then Monica Seles (2), Nancye Wynne (2), Arantxa Sanchez (18), Hazel Hotchkiss Wightman (20).
Now we need old fashioned pictures!