Neat idea. I was thinking Russia would count due to female rulers like Catherine the Great, but after looking at the link in the caveat I see this is just for elected/appointed rulers rather than monarchs.
Yeah, this is for after countries become independent or gained their current government/borders. I think if you tried extrapolating it to old empires, almost every country would have had a female ruler at one point (or at least a strong female authority figure like an empress or queen).
Hmm. For some reason the Wikipedia map did not list the Netherlands as having had a female Head of State. But upon further research, I agree with you. I've replaced it with something else. Thanks for correcting me!