We at Michigan State University have opted to use only the enum/chron field in
item records because it facilitates the circulation process.  We use a weely
tape load of all of our cataloging.  Pieces cataloged, for example, this week,
will not be loaded and indexed in our database for 2 weeks.  Because of this
delay we often need to create unlinked item records to allow a piece to
circulate before the bibliographic and copy holdings record loads.  The
information that is put in the enum/chron field (vol. no. year, etd.) will
show up in the call number index.  Information put the midspine field will
not. The use of the enum/chron makes it easier to locate and link the item
when the reord is loaded and/or the piece returned to the library.