This confirms what we knew already, its the original stock, or one that perfectly fits, which is practically an impossibility.
Glad you have a handle on disassembly, some experienced collectors make mistakes and they are easy to make if its not been apart for decades. Once you get it apart, confirm the internal serial, it would be interesting if the error was carried over inside. Also, check out the barrel code, it will be under the barrel, near the barrel shoulder (near the receiver), it should have a fireproof, three acceptance stamps and an barrel code, probably "BS" followed by a number, in this range high 600's or low 700's are consistent, but it can range widely. Probably low 700's for this serial range. Again Mauser is very consistent in all things, even during the war, but variations do exist.
Glad you have a handle on disassembly, some experienced collectors make mistakes and they are easy to make if its not been apart for decades. Once you get it apart, confirm the internal serial, it would be interesting if the error was carried over inside. Also, check out the barrel code, it will be under the barrel, near the barrel shoulder (near the receiver), it should have a fireproof, three acceptance stamps and an barrel code, probably "BS" followed by a number, in this range high 600's or low 700's are consistent, but it can range widely. Probably low 700's for this serial range. Again Mauser is very consistent in all things, even during the war, but variations do exist.