Saint-Loup's predecessor as commandant of Jülich-Juliers, Barrère, was a colonel in 1810:

http://books.google.de/books?id=O6hCAAAAcAAJ&pg=PA268&dq=barrère

I couldn't find him in Six, so he probably remained a colonel until he was replaced by major Saint-Loup. I haven't got Quintin to check what happened to Barrère.

Was there something like provisional promotions which had not yet been confirmed by the Emperor ? Or a promotion without brevet ? Maybe Saint-Loup was temporarily promoted général de brigade, to place him in rank above Barrère ?

I still wonder how a major Saint-Loup could pass as a general.