45cat/45worlds Album/record/cd pages refer to all versions of a release with the same catalog# (sure for many there's only 1 version, but for some like example below there are more than one..and i've even had some 10cc singles that have a half dozen MB releases mapped to one 45cat page)

http://www.45cat.com/record/dm269

This maps with our concept of release groups not releases, however 45cat/45world URLs are only allowed on a release level and not the release group level, where the opposite should be the case.