Both the Birmingham and London proof houses stamp an "R"stamp at the forward(muzzle end) end of the barrels flats when a gun has been re-proven. The photograph of the flats of the Birmingham made replacement barrel for the subject Holland Royal does not have the "R" stamp. (Or at least it was made by a Birmingham trade trained barrel maker) Whilst I suppose that a gun could be re-proven and not stamped (in error), I have not encountered such a mistake. They do make mistakes and I have encountered a gun re-proven that had the barrel bore stamps reversed from right to left. One is in my shop, just now.

Bv