Found a minty copy of this at the boot the other day...
(£8... little more than I'd usually spend.. as I'm a cheapskate... but hey... it was worth the extra dooh!)
...Anyway, the point of interest here is that I had to ask the guy selling it to get it out of the plastic sleeve it was in, which he couldn't as the plastic sleeve had shrunk around the album, so he let me cut the sleeve off to look at the album, saying "It hadn't been out of the plastic since the first, and only play at time of release"...
...And this is interesting, because according to Record Collector Price guide, this quad version never had any inserts, that the standard stereo issue did, but it did occur to me : "I wonder...", so I took the record in it's quad inner out of the sleeve, opened up the sleeve a bit, and hey presto!:
Both of the stickers fell out!
Of course, no posters, but most will know, this gatefold for Dark Side has one closed end, so to see if anything is hiding in that side of the sleeve, you'd have to do what I did, and open out the sleeve a little, and look from one end to the other.
My point is, that I wonder if these Quads did get issued with the stickers, but where people don't think they have them, could they be hiding in the Dark Side of your Gatefold?
...If that describes your copy, got to be worth taking a look eh?