It wasn't until 1933 that Brecht finalized the names of several character. For example, in the premiere at Leipzig, the protagonist's name was Johann Ackermann, but it seems that in some other early production it may have Paul (or Paule) Ackermann, In later productions, his name was changed to Jimmy Mahoney. Some German-language productions have restored the character name to Paul Ackermann.
The character who would later be called Fatty the Bookeeper (or Fatty, der 'Prokurist') was known as Willy, der 'Prokurist' at the Leipzig premiere and some of the other early productions.
In the original Leipzig production, several characters had different names than we know from later versions, as you can see on the cast list for the production.