hello Barry - regret to say that images of British Board of Trade design Registrations are available only from The National Archives in London. I believe that researchers employed by this facility will carry out investigations for you, but this is expensive.
However, there are one or two published books which provide a list of those numbers allocated to glass (CLASS III), and these books include other details such as........date of Registration, name of manufacturer/registrant.
The absence of an image does lessen the usefulness of such information, but if you have just the occasional request, I'm sure we can probably assist with a picture.
Don't think that your mystery seal will be of any help in relation to these Board of Trade Registered designs, and regret to say you won't find this information in Canada.
Using one of the books which lists these Registered Nos., you could scan through for James Couper & Sons, but regret I've no idea if other numbers occur, for them, additional to those three we've discussed above.
Registration (in the U.K.) started about 1842, and continued in one form or another, I think, until more or less the end of the C20. We have others here who are far more knowledgeable on the history of Registrations of British pressed glass, and they may wish to add their thoughts here.
Other countries had similar systems I believe, but the numbers we're discussing in this thread refer to glass made within the U.K. (there are exceptions I believe where some Continental made pieces imported into the U.K. - are Registered in the U.K. to a British based Registrant).
Of the Books referred to, you may find the following of most use (covering the Victorian period almost entirely) .........
'English Pressed Glass 1830 - 1900' - Raymond Slack - pub. 1987
'The Identification of English Pressed Glass - 1842 to 1908 - Jenny Thompson (plus the Supplement).
and following on from those two is......
'The Glass Association - Registration Numbers 1908 - 1945 (referred to usually as 'The Blue Book) - because it's blue

Unfortunately, specialist books like these are often expensive - and occasionally out of print, so be prepared for disappointment.
You didn't mention contacting Brian Brooks (is he no longer with us??) - hope you do get a reply from Jeanette Hayhurst.