Otherwise, the historical record is full of names that have survived into the present day, like Teresa, María, and Juana. Much more exciting to find are the ones that haven't had much impact on the present day, such as
Flammula ("little flame," quickly morphed into "Lambra," the villainess of SNKL)
and my all time favorite, Urraca
There was a Queen Urraca of Castile for a while who deserves several novels, and another Urraca has a role in one of the historicals I'm researching now. Best of all, "urraca" is the modern Spanish name for the magpie, a bird I have always found mysteriously breathtaking.
In the course of that research, I found out something disturbing about one of of my main female characters: I'd been calling her the wrong name the entire time! Gonzalo Gustioz's wife Sancha, so called in the histories and poems, went on the record in charters and donations with the name Prollina.
I was disappointed because the next book I want to write has a main character also named Sancha, and if I could have used a different name for the SNKL Sancha, it would be less confusing all around.
But then I got thinking why the poets changed the name. Sancha means "holy" or "saintly," which is perfect for this long-suffering mother of seven warrior sons. And Prollina, no offense, isn't very pretty. Storyteller's prerogative strikes again!