I will provide my personal feeling after my own research that the number on the bayonet has been period redone
I am going to explain me...
The fact is the bayonet and the scabbard are matching WKC 1937 with same number (5911 j).
I think we need to look closely at the markings of the bayonet itself :
The "N" of Nordsee and the "k" on the right of the number we can see are very faded and not the number, as this one was unreadable (certainly after big and long time of use, for a 1937 dated bayonet, I think it's logical), the period owner or the period company gunsmith has redone this number for be more readable. It's why they are different style of numbers.
The markings on the scabbard are IMO intact because they were protected by the leather frog, it's why they are less used than on the bayonet.
Also I have seen a lot of WKC 1937 bayonets who were issued to the kriegsmarine units and they are all with 4 numbers.
Anf finally I think this is a period legit KM used bayonet.