Hi @timgunn1962 - very much a manufacturer label (serial number mangled in the photos intentionally):
The shelves were some kind of metal, but the owner found that when using them for glass, they'd release a very fine powder (looks like metal filings - they're in the base of the kiln), as such they'd ruin some of the work that was being made in the kiln. So there are also ceramic shelves that come with it, thus mostly removing the issue, but the rack the shelves go into still releases the powder (whatever it is). It is also over 10 years old, so it may just be generally a bit worn out!
It's a very good suggestion that it may just be the shelves and the rack that limit the temperature (though it seems they were failing well below 1000C, given the powder), so I'll give Essex Kilns a buzz and see what they say about it.
Thank you again for your thoughts.