I'm a cataloger and I work with rare books where differences in editions are important, so yeah, I would. :)

There are cataloging rules that say how different something can be before it is considered to be a new edition rather than just a reprint (rare book catalogers and catalogers of special collections argue for more) which means a new record -- when I'm cataloging a book I can put different reprints on the same record with the original with a note that identifies each as the original or a reprint, but something being officially put out in four volumes instead of five would need a new record even if the text is the same.

I did have another title that was originally published in one volume that I got in two, but that was a case of being bound differently; the second volume had a handwritten title page and obviously had not been published with the intent of being in two volumes; that one was an exact printing (or reprint, if there was more than one printing) of the one volume version and went on that record with a note that our copy was bound in two volumes instead.