Part of my ancestry is of Ostfriesen heritage, coming from the extreme northwestern area of Germany next to The Netherlands. Up until approximately 1811, the patronymic naming system was used. That is, the surname changed with each generation and was a derivation of the given name of the father. Unlike the Scandinavian countries, the suffix son or dotter was not routinely added. However, at times sen was used, i.e., Janssen. Women retained their surnames at marriage.
In this photo of an entry from the Rorichum Ortsfamilienbuch, one can see the following surnames were all used in this family: Sÿbolts, Siebolds, Veltkamp, Harms, Wortelke, Reemts, and Siebels. No wonder genealogy is a challenge! Maybe that’s part of the reward!