Bayonet Translation Help Needed

[Akira Komiya]

Although the character "補"= ho can have connotations indicating auxiliary or substandard, as in "兵補"= foreign auxiliaries recruited in occupied Asian countries mainly as laborers and security guards almost in the same manner as the German Hiwis", Hilfswillige in WW2, I have no idea what the combination of the character with the character "穴", ketsu= which means hole could mean.
Since you write that the bayonet itself is untouched and Kiipu says that the same marking is seen on other rocking star bayonets, it is possible that it is an acronym of a school or other institution's name with "穴" being the first character of the institution's name (most likely the town or city's name) and "補" indicating the type of institution.
However, there are tons of towns whose names start with "穴" and I have no clue what "補" used in the context of an institution' name could indicate.

[Jareth]

As already mentioned I’ve only seen this stamp on Rocking Star and other naval trainers

[Akira Komiya]

I am still at a complete loss as to what the markings "補穴" or "穴補" could mean, but I found that another bayonet bearing the same markings had sold on an auction site here last year. Yahoo!オークション - 実物 美品 旧日本軍 三十年式銃剣 『補穴』刻印 ...
You can see that in this example there are no maker's markings.
I was thinking that if the bayonets bearing the markings were limited to those intended for the Navy, they could have been issued to guards of a Naval supply depot bearing a name starting with the character "穴", thus "補穴" but now that an example turned up which appears to be completely civilian, I must admit I am totally at loss what the markings mean.

[Bobby]

Thank you Akira. Interesting that you found another Rocking Star with the same markings. Kiipu and Jareth have noted seeing the same markings as well. I just did a Google search and found another Rocking Star with these markings. At first I had been thinking that the markings had a possiblity of being added post-war. But that now seems unlikely. I have attached images of the Google search Rocking Star. I note that the arsenal stampings on the blades seems to vary in thickness/fineness from bayonet to bayonet.