John made the following comments on 6th September 2017.
Since the article was written ( my goodness, was it really 24 years ago, how time flies ??!! ) some more gen has emerged and the article needs modifying appropriately viz; there were no medallions struck in silver for the officers, they were all bronze when awarded and some were plated later for the recipients, some silver, hence the confusion and some mercury gilded, additionally some had details engraved in addition to the already engraved May 31st.,1916 , names, numbers, Battle of Jutland etc , some round the rim and some on the blank space on the reverse.
They were apparently struck by Spinks and supplied by Browns the Jewellers of Chester; they are no longer in biz.
Since the article about 25 medallions have surfaced.