I see two main possibilities.
First, your safe might not be a Mosler; I’m no expert at spotting them unless the name is painted on. Numbering the handle was not common, but I believe there is at least one other maker who did this, and I’m not aware of any numbering records aside from Mosler’s (and I can’t remember the other maker).
Second, the entire number may not be visible. I can’t tell for sure, but might the paint be hiding something?