Women Pilots, from W.1 to W.168
When the Women's Section of the Air Transport Auxiliary was formed in 1939, they looked around for experienced British Empire women pilots.
Well, there weren't very many. According to one of the best of them, Gabrielle Patterson, this was because up to 1938 "women pilots hitherto have consisted only of those with large enough bank balances".
Gabrielle had then helped to set up the Civil Air Guard, which offered subsidized flying lessons for the less-well-heeled, but many of their pupils hadn't even managed to complete their 'A' Licence before all civilian flying was stopped at the outbreak of WWII.
Anyway, after a while, the ATA found that they had run out of women with 250 hours, then 150, 50, and eventually they decided that they would have to train their own pilots from scratch. And even then, they had to import some Americans!