MNCAT is our library of record, not WorldCat. For various reasons, WorldCat is an unreliable guide to what the University Libraries holds. For more detail, read on.
The libraries do all our original and copy cataloging and catalog maintenance in MNCAT, our local catalog. We regularly export batches of records to OCLC and RLG, the two bibliographic utilities to which we belong. However, this does not mean that OCLC's WorldCat and RLG's RLIN database accurately mirror what is in MNCAT.
OCLC does not load all records immediately. OCLC's matching algorithm is fairly complex, looking for multiple points of consistency. When such things as title, year of publication, ISBN/ISSN, publisher, and system number all match up, OCLC promptly and reliably adds our holdings symbol to their WorldCat record. However, if there are discrepancies, or if the record is new to OCLC, it is shunted off for manual review, which can be very slow. Consequently, original University of Minnesota records (e.g., for theses) are often not found in WorldCat, or may be long delayed before finally appearing there. Also, OCLC does not routinely remove our holdings symbol when we include "deleted" records in the batches we send, so many of the titles we appear in WorldCat to hold have actually been withdrawn or lost, as indicated in MNCAT.
Prior to our move to Aleph, RLIN was a more accurate mirror of MNCAT, because RLIN maintains a copy of each RLG member institution's record. While in NOTIS, we would routinely batch update our bibliographic records in RLIN whenever changes were made to the bib record in MNCAT. Since moving to Aleph, we have limited RLIN updates to cases where the MNCAT holdings record has been added or modified; so heading corrections no longer prompt an update of the RLIN copy of our record. Still, RLIN and Eureka are currently a closer reflection of MNCAT than WorldCat.
MNCAT is our library of record. MNCAT should be consulted to find out what we hold, and where it is shelved. When WorldCat indicates that we have a record but MNCAT does not, WorldCat is wrong in the vast majority of cases; and many of the titles we do hold do not and may never appear in WorldCat.