Here's a site that will show you a graph of the popularity of your name. I can't get the image to show up, but Nancy was popular from about 1950 to 1965, with a very steep rise and steep drop. And, of course, you can put in your own name and see how it's been doing.
There's a map of when my name peaked in each state, an animated map for maximum popularity per state, and a field for theories about why a name was popular when it was. I have no idea for my name. It seems to me like an equally good name for all eras, but what do I know?
The name search feature is fun, and I expect it's driving traffic to Vintage Reprints.... but I can't quite figure out what they sell, or how to get to the name search from the home page, or whether there's a public list of people's theories about name popularity.
I have no idea if there are names that just sort of putter along at a stable level instead of peaking.
Are authors careful about giving their characters probable names? If an author isn't, does it bother you?
Going farther afield, I have no idea how (at least for me) GRRMartin got away with a fantasy which has no obvious connection to our timeline with characters who have a mixture of contemporary names, common names with weird spellings, and totally alien names. He put work into culture-building, but that doesn't explain why all the names aren't alien.
The Natural History of Dragons by Marie Brennan, a book that I mostly liked, made me crazy on that issue-- it's pretty much our world with dragons added. The countries are similar to real world countries, but the names of the countries have no resemblance. The characters have real world names.
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