Brian â€” the Glass Association journals are invaluable. As a member, you can obtain photocopies of any which are out of print.
For example, Vol. 2 contains Barbara Yates' article The Glasswares of Percival Vickers & Co. Ltd., Jersey Street, Manchester, 1844â€“1914
, which contains material relevant to you explaining that Thomas Percival was the nephew of Thomas Webb Snr., becoming works manager for Molineaux & Webb before setting up in business in his own right.
All three glassworks (the above plus Burtles Tate) in Manchester had family connections, and cooperated to a certain extent, so Yates found at least one example of one glasswork's products filling gaps in another's product range, a practice which I suspect happened a lot more than we know about today. Of course, with cut glass, it is more complicated, as uncut blanks could have moved from one glassworks to another.