While working today, a reference librarian handed me a problem. She had a patron come up to her and ask for the "Sacra Pagina." He was not talking about the Bible, but rather an 18-volume commentary, prepared by an international group of scholars, of the New Testament. When the reference librarian looked online at our catalog, she first searched by "title keyword". Eleven titles came up. And not the specific one the patron was looking for (he was looking for the Gospel of Luke). So she did a series keyword search. All eighteen records came up, including Luke.
So she sent me an email, asking if this problem was "worth fixing?".
I hate it when local practice gets tied up in OCLC. At our institution, since we are relatively small, we do not do a lot of cleanup to the MARC that comes down to us from OCLC. We check for subject headings, good call numbers, and sundry, but our copy catalogers do not typically check for the appearance of 830s when they see a 490, or check to see if it's appropriate that there be an 830. We do rely on OCLC and "good" copy to get the records we need.
In this particular case, I could see the multi-volume set being cataloged as one work, with 18 items attached, and no series entry. Or it can go the other way: 18 works, all with 490s and 830s, and one item apiece. In OCLC, both options are represented. However, whether or not there is actually an 830 depends on who created the record. DLC definitely put in the 830, but they only created three of the eighteen individual-volume records. The only reason I see for not putting in the 830 in this case is that some institutions felt that they needed 830s and others felt that they didn't need anything beyond the 490. And then OTHER institutions decided that it should be cataloged as a multi-volume set under a single title. For the record, when I did some research on when it's appropriate to use an 830, it became clear to me that this multi-volume work definitely merits an 830. As is often the case, Library of Congress was correct in its assignation of MARC fields.
"Cataloger's judgment" does not do justice here. I feel that this is has to be a case of local practice influencing the judgment of catalogers. And I get it. If you are an academic library at an institution that does not do a lot of theology, you would be much more likely to catalog this thing as a multi-volume work with a single bibliographic entry. Who needs lots of records for this one thing? However, if you are at an institution where theology is relatively important, you are more likely to make each volume its own record, since a researcher looking for the Book of John would probably search for Book of John, not Sacra Pagina, no matter how famous the Sacra Pagina is. Unless you happen to work for an institution where theology is very important, and the researchers know exactly what the Sacra Pagina is, and if you have unreliable 830-placement it means that they can't find what they're looking for when they do a title keyword search.
And other librarians here wonder why I claim to have such a very long training period for my copy catalogers.