While dealing with this issue at the moment, I raised this agonized question one more time at the MBZ dev IRC channel:
<zazi> one release can different catalog numbers
<zazi> a catalog number can have different releases
<ocharles> A release has multiple release labels (label/cat no pairs)
<reosarevok> zazi: all the labels and catalog numbers for a single release are supposed to be related to the same country-date (that is, the actual CD or whatever was published as a cooperation by two or more labels, or the label gave it several catalog numbers)
<reosarevok> (also, a catalog number can be in different releases, for example if the label gave the same catalog number to the CD and vinyl editions)
<reosarevok> (but AFAIK it doesn't link them in any way in the database, it just means they happen to have the same info in that field)
<zazi> yep, that's what I thought as well
My conclusion is that we should move the domain of mo:catalogue_number and mo:label to mo:ReleaseEvent instead of mo:Release. Any opinions?
See also  for an earlier discussion at the MO mailing list about this issue.