Speaking strictly of vinyl here, particularly pre-CD-era vinyl.
Matrix code "variations", within the bounds of the guidelines, can indicate a completely new master cut by a different mastering engineer. But albums with significant print runs will have new labels printed (and therefore new typesetting, resulting in differences in font size or text alignment) multiple times during their time in print with absolutely no other changes. If a plant runs out of A-side labels before B-side labels, you can end up with three "unique" releases—old-A+old-B, new-A+old-B, and new-A+new-B—based on what is arguably a routine, expected manufacturing variation. That means extra time required to find the "correct" version of a release and more time required to create one if your particular label tweak isn't already captured in the database. (I have dozens, probably over a hundred, in my "to add" queue at this point, and I've barely even started—largely because after going through a half-dozen or so records, each of which has three or four or five possible candidates whose 600x600px images all have to be painstakingly compared, I look up to see an hour has ed and decide to move on to something else.)
I can see different label blanks as a good signifier of "uniqueness", as that can give a rough idea of when an item-in-hand was manufactured. But a completely separate entry every time an intern at the print plant lays out a new version of the label with the same information in a slightly different format, that I don't get.
I would argue the cost of this rule outweighs the benefit and would like to know what others think.
