Ever heard of the Tiffany Problem? It refers to the issue of historical reality confounding our expectations. Tiffany was a real medieval name (a variant of Theophania). It shows up at least as early as 12th century Britain and France, but try naming your fictional medieval character Tiffany and watch readers stumble on the perceived anachronism.
Youtuber CGP Grey went on a research adventure to try and figure out how the name got from the Byzantine empire over to English and when the first “Tiffany” used that spelling. He also shares a (much longer) warning about the perils of getting too deep into the details in the research process.
The term “Tiffany Problem” seems to have been coined by Jo Walton. It has been mentioned on MetaFilter a couple times before. See also: “Reality is Unrealistic.“
I’m sympathetic to CGPGrey losing his mind over the dating of the Tiffany poem, because I have spent a disproportionate amount of time trying to figure out if Terry Pratchett knew Tiffany was a legit medieval name when he proved that every writing rule has an exception and gave it to Tiffany Aching.