See post 35 on 29th Sept where Nicola writesA tweet from the publishers tells me that the publication date is next week (Thursday I think) so whoever you got it from is being rather naughty! As usual, I've got mine on order from WildSounds.
'Showing as 'In stock' now on NHBS '
and post 38 where S Dog has had his / hers since Thurs last, from Wildsounds
I regularly find that titles are available with some vendors, before the official release date, no idea of the mechanics or rights and wrongs of it but don't think there's anything 'naughty' going on?