Well, Lindy, separate the question of unique forename spelling from the question of what is actually (proably, IMO) a cultural question of "suitable names for boys / girls". And from the other issue of mis-spelling due to typo errors.
WT is global or aiming to be global. Global indicates numerous cultures which have their own "suitable names" roster. Or if you prefer "the usual sort of names used" ... in some eras in the USA and what was going to be the USA, Sarah, Mary, Martha, Jane, Ann / Anna / Anne, Lucy, Nancy, Elizabeth and such were the usual sort of names used ... names have a trends or are more commonly used during certain periods of time such as Lynn / Lynne, Lindsey, Loraine, Lana, Belle, Bessie, Betsy, Beulah, Caroline, Carolyn, and such ...
Cultural / national conventions which add the suffix for "son of" and "daughter of" are often found.
And as has been mentioned, the computer is programmed to check unique spelling with the PM in order to determine if the PM has made a typo (typed in the information incorrectly). I noted one case recently where Sarah had been typed in as Srah. Records indicated it was indeed Sarah and not Srah.
Traditional use over time has in fact assigned a number of names as "male" or "female".