Re: World Hard Court Championships was a Grand Slam event?
1Until 1923, the French Championships were open only to French nationals. The World Hard Court Championships (WHCC), actually played on clay in Paris or Brussels, began in 1912 and were open to all nationalities. The results from that tournament are shown here for 1914 and from 1920 through 1923. The Olympics replaced the WHCC in 1924, as the Olympics were held in Paris. Beginning in 1925, the French Championships were open to all nationalities, with the results shown here beginning with that year.
And Lenglen's major haul would be the same even if you exclude WHCC and swap in the closed French championships--12. There's no double dipping involved. I don't see what the problem is. The WHCC was a much bigger event, open to anyone, and tennis historians credit that as France's "major" during the time frame before the french championships were open.