WRT counter sales at Titchwell Birding World has a sale or return policy. When I was at Baguette Bay it was tried and failed, just a right ol' p in the a to repackage 'em and send back each month. I suspect one of the editors can easily drop into Titchers once a month. BB simply can't afford this type of approach.
The following is facts are probably misquoted through rough memory of a talk I attended a few years back, but will give you an idea of what they're up against. BB suffered horribly under the old management regime coming close to closure at the start of the decade and having to be saved by small group setting up 'BB Ltd'. It has struggled to increase a circulation of what was (four/five years ago) in the region of 2-2,500.
Birding World was doing quite a bit better than this, but only about the 4-5,000 I was led to believe. It obviously gained readership from BB, taking a lot of the rarity oriented, being much more up to date, topical and opionated.
'Over the counter' mags were thought to be i.r.o. 9,000 pm for Birdwatch and 20,000 for Birdwatching. The latter had been as high as 23-24K but slipped back to about 17K when they had the audacity to cut down the number of pages dedicated to garden birding. This is why you suffer so much of the "ooo a jay on the bird table" guff, and similarly why there's yet another bino review and a 'wow look what's new in gortex' report. Oh, yeah, and the editor's just been on a holiday you can go on next year for three grand. They're like the ITV of the world. You want to be able to pick up at the shop, sure, you can, but you're going to have lots of ad breaks.
BB will continue to struggle against BW for rarity celebrity gossip, against Birdwatching for lack of lowbrow coverage and against Birdwatch for its slightly higher browed coverage of i.d., etc. IMO where it still excels is in trying to bring together national snapshots (rarity totals, scarcity totals, rare breeding bird totals, etc).
It is certainly the one of the four mentioned I find myself referring back to the most, and I would say if you haven't seen a recent copy, do get hold of one. I think NHBS has individual issues listed for sale, but I stand to be corrected.
(And while you're at it, you might want to try to get hold of BTO News. That's one magazine that always has something worth reading and worth keeping. Certainly worth a BTO subscription on its own.)