Well, I like to take it to mean that witches have owned the Elder Wand, but they just chose not to advertise it to the world. It is clearly a bad idea to tell others that you have an unbeatable wand, and witches who have owned it may have realized that and chosen to keep quiet about it.
Because, you know, men tend to like to gloat about their power whereas women do not always feel the need to do that.
No offense to any men, and I'm not saying all men are like that, but history has shown that men like to flaunt their power.