Ah, thanks for that. My first thought was that it must be an error, but there were just so many of them - and
Mary, and various others, are listed as boy's names in rather a lot of the US popularity charts, so I just had to ask. I guess this sort of thing just slips through on any large collection of data: an ancestor of mine is listed in the 1881 census as 'Hammerley' which is the weirdest transcription of
Emily I've ever seen. :)