Oskar,

The short answer to your question is probably but not necessarily.

A good example is my SKB over and under made in Japan but bearing British Proof marks.

That at is because that when it was imported Japanese proof (I think not carried out at an official proof house but at the factory) was not recognised by C.I.P. or the British proof authorities.

The same applies to American made guns imported into this country, unless in transit they have been Proofed at a C.I.P. recognised Proof House.