Yes, the English Heritage information appears to be correct, as does the comment in CH 20th Century British Glass (both quotes shown below for completion).
And we now have an example of c.1927 for the date the brand name Royal Brierley Crystal was used on a vase (etched on to vase).
As quoted at the beginning of this thread:
'According to this information from source - English Heritage:
http://www.britishlistedbuildings.co.uk/en-488295-royal-brierley-crystal-works-
it states within that information that
'The patent for "Royal Brierley Crystal" was taken out in 1926 and subsequently became the company's brand name.'
So we have a date that they took out the patent for the brand name.
However it doesn't give information as to what date that brand name started being used.
'HISTORY: During the late 19th century, Stevens and Williams became renowned for the quality of their engraving, in particular intaglio work, on crystal ware. In 1919 the company were awarded a Royal Warrant by King George V, and the works were visited by the Duke and Duchess of York, who later became King George VI and Queen Elizabeth, in June 1925. The patent for "Royal Brierley Crystal" was taken out in 1926 and subsequently became the company's brand name.''
And from CH 20th Century British Glass as quoted previously in this thread:
'Page 151 ...
'The brand name 'Royal Brierley Crystal' was adopted by Stevens and Williams in the 1920s who saw their glass as a royal product.'Not that it matters but I'm idly wondering if these trademarks as commented by Christine earlier in the thread (see quote below), were trademarked for the use of capital letters for the name as well as just using capitals at the beginning of each word? otherwise someone else might appropriate the name using all capital letters. Is that how these things work?
'
According to the Intellectual Property Office, ROYAL BRIERLEY CRYSTAL
was trademarked in 1967 and was owned by Royal Brierley Crystal Limited
(Royal Brierley CRYSTAL
was trademarked in 1988 by Dartington Crystal (Torrington) Limited
who also trademarked ROYAL BRiERLEY
in 2006)'