Well I agree the whole thing makes no sense.
Company's such as Jules Lang of London would import items from the continent and register them here in the UK, items can be found with English Registered Numbers which on the listings show as registered by for instance Jules Lang, when in fact the glass was made overseas. So the registered number mark would be in English ie RNo.......what is strange here is that in all the items I have seen that have been imported and registered with a UK No I have never seen the originating company's trademark or any other mark alongside the Rd No.
It was only that Oetel Glass used this mark that made me wonder, I do have to agree with Frank they were not known for their pressed glass (although they did produce it) and their early glass tends to be of high quality.
Unfortunately I cant photograph the mark, I struggle just to read it as it is so worn and on a curved surface so a photo would be impossible. What I can say is that it is a 5 figure number which would date the item between 1884 - 1888 which looking at the style and the wear on the base of the item seems about right.
I suspect this is one of those mystery's I will never solve, I just wondered if anyone else had come across anything similar.
Regards