Thank you for your swift and informative reply, Anne.
So, yet another 'missing' Hoskins, Rose & Co. registration run to ground.
I strongly suspected that, if the regsistration number was in the Blue Book, that they (or another importer) may well have been the registrants because... I've now checked the pre-1958 Libochovice catalogue on Marcus Newhall's Sklo Union CD-ROM and, surprise!, the jug appears on page 38 as pattern number 1498.
I will lodge the photo and details on the GMB RD numbers database shortly.
Is this another case for transferring the topic to the GMB Czech etc. section for posterity?