Well, plenty. The Dictionary of Medieval Names from European Sources provides documentation for first (given) names from numerous sources. It traces the appearance of names from 500 to 1600 as they appear in various countries. The diversity of the spellings of names is never more evident than in this tool; for example, “Frederick” and its many variants are cited hundreds of times from dozens of tomes. This site also gives the date of the first appearance of a name (or its variant) in the countries examined so far. Western European sources have been culled for their information; Eastern European sources are now being scrutinized. All in all, a fascinating project showing the richness and history of names and their development over time. FYI: It appears that the first mention of “Frederick” occurred in 814 with the spelling “Friderici”.
What’s In a Name?