It can seem to be a bit of a mystery as to why some books got dust jackets and not others. Number 48 is obviously a film tie-in and some are in the later PAN cover style which I suspect is really just a way to shift old stock. It was also a surreptitious way to raise the price as it often higher on the DJ than the cover but why are there two very similar DJs for number 90? My biggest disappointment was on finding the DJ for 138 was exactly the same as the cover.