Most of these are location codes for other libraries which came in as part of records from RLIN. We don't need them, but they're hard to get rid of. For more detail, read on.
Aleph uses an expand program to copy the 852 on holdings records linked to a bib into the extended version of the bib record--the one that appears in the lower Cataloging pane when you search, select, and click Show. This 852 is used to create the various call number indexes, and needs to be indexed. At the same time, many of our old RLIN records have retained a bib 852 for the original inputting library. These numbers have converted with the same coding used in our local bib 852s; so these codes appear in the index, too. For example, the code "sml" converted as a Yale sublibrary code, so if you do a LC/NLM Shelflist search for beginning "sml ..." you see lots of Yale 852s.
We don't need to retain these, but neither can we eliminate all the bib 852s, since the local ones are necessary. From time to time Database Management has had a student working at deleting the bib 852s for non-local institution codes, but that takes a certain familiarity with our local codes; and since the public call number indexes are not prone to displaying these, it's a low priority problem.
They really only appear in the Shelflist indexes, where Aleph includes the 852 $b $c in the index string. If the search you do in a shelflist index begins with a local sublibrary/collection code combination (e.g., twils gen ...), these old RLIN codes aren't a problem. They only appear when you look past the numbers beginning with local loc codes. Again, that makes these lower priority for maintenance. Still, it's annoying to see these pop up, and eventually we'd like to get rid of them.