In German society there was a first name and a calling name, so John Jacob would have that name on church records, deeds, etc., but for anything else, he would be known as Jacob.
There was a naming order for families. This was observed especially with the Mennonites. The first two sons were named after the child’s Grandfathers. It was usually the father’s side first honored unless the Mother’s father had died before the Father’s father and the Father’s father was still living. The females were named in like order. They believed in honoring their fathers and mothers. This naming order started to go out in the 1840’s.
Nicknames can also cause trouble. These are some among the Pennsylvania Germans. Anton (Anthony) was nicknamed Tunis. Barbara was Bevvy. Dietrich became Dieter. Elizabeth could be Eliz, Eliza, or Lis. Johannans was Hans or Hannes. Magdalena became Matti, Matta, Lena, or Molly. Maria was changed to Mary with the nickname of Polly or Molly. Nicholas (Nicholaus) was Nickel or Claus. Anna or Ann had the nickname of Nancy or Nan. Catharina was kate or Katie. Christoph (Christopher) was Stoffell and was confused with Christian whose nickname was Christ or Christli. Gottfried (Godfrey, Geofrey, English) was confused with Frederick with the nickname of Fritz. margretha was nicknamed peggy or Maggie. Valentin (Valentine) became Felty. Fronika became Fanny. Ludwig can be Luwick or Lewis. Bernhare, Bernd, and Barnet became Bernard.