I've spent some more time experimenting and come to the conclusion that Zotero is not behaving consistently with the Princeton theological library website. Sometimes it downloads the call number and sometimes it doesn't. For instance it downloads the call number for https://catalog.ptsem.edu/record=b1048112~S1 but not for https://catalog.ptsem.edu/record=b1065858~S1. Am I doing something wrong? The call numbers are important because I want to use Zotero to catalogue my books. I'd rather not duplicate programs if I have to, but if I can't get Zotero to give me call numbers for the books I have, I'll have to switch to something different.