N-25 would mean that the knife is either:

A) A Model #25 (Trapper) with nickel silver and aluminum hardware.
B) A Model #26-4" with a #25 handle.
C) A Model #27-5 3/4" with a #25 handle
D) A Model #12-9" with a Model #25 handle

B-25 would be the same as above with all "brass" hardware.
Hope this helps, Capt. Chris