Anne - unless the people at Kew have changed their system (and I haven't been into the thing in detail), their method - on the pc screen - had always been to show many large groups of Rd. Nos. - and not to show data down to individual No. level - since obviously there is a vast quantity of data relating to Rd. Nos. (not only for glass, but for all 14 or 15 other groups - additional to glass).
You identify the range of Nos. which will include the specific item you are interested in, then (either by phone prior to arriving, or in person when you arrive) you request the Register (text details) or box of Representations (the pictures) - and they try to have them available within the hour. For glass these are BT 52 and 53 from memory - (BT standing for Board of Trade).
None of this is possible, of course, unless you are have a reader's ticket - and for this you must visit in person and register yourself together with a photograph (and possibly a birth certificate, but I'm not sure now about that one).
If Kew have changed their ystem, and all this may now been done on the phone, please do let me know