According to the The Ross Rifle Story the Home Guard Ross's serial numbers fell into 1 of 2 clusters: 12125 - 12611 and then 13863 - 17977. By the end of 1914 15,850 MkIII rifles had been delivered and one month later, January 1915 over 19,000 MkIII's had been delivered in total. If the Home Guard MkIII's were taken out of serial production then they would have been manufactured between November 1914 and January 1915. The one's I've seen appear to be early production so this jibes with that time frame. Of course, I'm making some assumptions here but I'm lacking any hard evidence. It was reported in The Ross Rifle Story that the sole known dated Home Guard Ross MkIII was stamped 1915 so that fits.