Hattons appear to have had a strange way of deciding who got what and when. I too received 001-004 at the same time, and received 006 about a week later. At the same time their website showed 005 and 006 as "in stock" and available for sale, but I never received 005 and they've all now disappeared from the website. I await the arrival of 005, but so far in vain.
As others have already said, hopefully Dapol will realise that selling decent quality wagons at reasonable prices means that they don't sit around on shelves for very long. Perhaps they can force the other manufacturers to have a rethink about their recent price hikes of old models and over the top pricing of newer ones!