My two cents: Overstreet needs to clarify the difference between "horror, supernatural, weird" whatever. They just arbitrarily change things with that guide to suit themselves, it would seem, without any reasoning stated to their readership. It's like their philosophy is "We change prices every year without detailed description as to why Book X went up, so why not change other things when we feel like it, especially if it behooves certain people affiliated with Overstreet."
A good example, as Keith has pointed out, is the Eerie #1 from Avon. Just a couple years ago that book was NOT listed as scarce, but now mysteriously it is. If you follow PCH, you KNOW that book is NOT scarce. Seems to be one on eBay alone every other week! In reality I bet someone involved with the guide stockpiled a nice little stash before designating the change to "scarce" status.
Bottom line: there is no reason for any designation other than "1st horror this or that." Any other title is revisionist history in an ever continuing attempt to make EC look like the inventors of comic horror.