If you are talking about the surface blemish that I drew the red line around in this photograph...
Then the answer to your question is that this mark (which I presume was made, not by the number die, but by a receiver jig or wrench for installation of the barrel), fell within acceptable tolerances for finish surface blemishes and did not affect proofing, functioning, or readability of the marks placed on the gun intentionally.
Remember that 42 was the very near end of full time production and the urgency of wartime needs let thing like that blemish through that would never have been acceptable on a commercial weapon. If there is one thing that governments are headstrong about, it is accountability of weapons and their production. The mark you point out was probably the result of wear of the receiver holding jig and would have been a very costly thing to replace versus the replacement of a single number die, or a single toggle piece that was unacceptable...
I hope this explanation was helpful. It was not based on any published references, but on 40 years of examining Lugers, ...on my experiences as a gunsmith (many years ago!) and also more recent manufacturing experiences in industrial environments.