Here's another image from the Molineaux Webb pressed glass catalogue. Plate number 23 is a fairly well known Queen Victoria commemorative, probably dating to the Coronation of 1837. The catalogue itself dates to the early 1870s and proves this plate was in continuous production for at least 30 years.
This plate has a "W" mark on it (see photo). Other early pressed glass plates from this very early era may be marked with a "D" or "WR". The attribution story for these plates has changed over the years. If you have any books by Ruth Webb Lee on American lacy plate Sandwich glass, you will find this Victoria plate in her books. I'm not sure if she ever claimed it was American but we can see now that it is not.
Back in the 1970s the thinking was that these marks might represent the manufacturer, and if you have the book by Barbara Morris from this decade you will see she suggests WR = Webb Richardson. The V&A museum attributed a "W" plate that they received in 1970 to Molineaux and Webb using the same logic, but I believe they have that particular attribution wrong - it's not the same Victoria plate as in my photos here.
By the 1980s Hugh Wakefield of the V&A was happy to attribute some of these commemorative plates to unidentified British manufacturers.
The current thinking is that these "W" or "WR" marks represent the name of the mould maker. There was a community of mould makers operating in Birmingham in the first half of the 19th century and using the commercial directories of the day, we can say with a high degree of confidence that WR = William Reading, a prominent Birmingham mould maker. There is more than one possibility for the mould maker behind "D" or "W".
These moulds were distributed to glass factories in England and the near continent.
Much of the information above comes from an excellent article on these early plates by Siegmar Geiselberger.
You can read it in more detail - in German - via this pdf from the PK2008-3 edition of Pressed Glass Correspondence. http://www.pressglas-korrespondenz.de/aktuelles/pdf/pk-2008-3w-vogt-teller-wr-victoria.pdf