The Deutsches Reich Arbeitbuch was simply a record of employment and would be personal to any individual. What date is it? My guess is that this was a matter of attempts to hide illegitimacy, as was the story of Lebensborn. He was illegitimate but his mother had married/had a partner named Kampmann who had brought him up(?) and used his name but had not legally adopted him so he had to use his "proper" name on an official record. Just a guess, someone else might have something more concrete.