The numbers were usually scribed onto the bolsters when the knives were finished using a hand operated pantograph. They were cut using a diamond tipped point. There were brass number that were placed in the machine. These had a groove through them that matched their shape. You traced the groove with a stylus and this was transferred in much smaller form to the bolster. The problem was that sometimes the operator would slip, oftentimes at the end because you're pressing down. This slip would also transfer to the bolster as a scratch, which is probably what you have there. If it was really bad the bolster would have to be re-polished and the etch done over.
Eric
