Manufacturer code on C216 Bofors ammo box?

[Tool Editor]

I have a C216 box in the US and I'm wondering more about its history. Does anyone know who made these boxes with the I N manufacturer code?
And if perhaps these are rare? I haven't seen this stamping on any others I've researched.
Also, the stencil on the side says B4. Does any one know what that designates?

 

[NZ L1A1 Collector]

I believe the "I" means "Mk. I" and relates to the Box: C.216 Mk. I

Its possible N might relate to the maker?