If proofed prior to 1887 the barrel flats will be stamped with a number indicating the bore size. A .577 BPE would be stamped "25". A .500 BPE of the period would be stamped "39". A smaller bore would be stamped with a higher number. Here's a photo of the flats of my .577 BPE Henry (proofed 25 bore):

Anything proofed after 1887 will be stamped with a decimal number indicating the bore in thousandths of an inch. For example, my Gibbs .450NE (proofed .450):

In either case, if proofed, the flats will be stamped with something to indicate bore size.

Without more information I don't see how anybody on the forums can answer your questions. Certainly there was no .470NE made before 1887.

Curl