Chris I believe you may have your photos a bit mixed in this post. I think the shots on the right are a matching pair, so that makes it the Sanderson with the '15 reissue mark, going on the ricasso shape as well as the inspection marks, which are the same as on my Sanderson example posted earlier. So that makes it the Wilkinson photos on the left with the matching ricasso shape. But there is a problem here as the cypher should normally be placed above the makers name, as on the example shown below. Which side ricasso are these markings applied on your Wilkinson - I can't tell from the photos. Somebody may have made a simple mistake, or it could originally have been made as a volunteer pattern (without cypher) and then had it added later, and it went on the wrong side. Bit of a strange one - but have another look and let me know if I'm on the right track, either that or I'm totally bamboozled.!!
Obverse of the Wilkinson showing wartime ('15) reissue date on that side as with p1907s, but no date/cypher visible on the front side