Dustjackets

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.
PAN 24 from 1948 Cover Artist ?	PAN 24 from 1948 Dustjacket Cover Artist ?	PAN 27 from 1948 Cover Artist Ursula Leacock	PAN 27 from 1948 Dustjacket Cover Artist Ursula Leacock
PAN 29 from 1948 Cover Artist ?	PAN 29 from 1948 Dustjacket Cover Artist ?	PAN 30 from 1948 Cover Artist Bruce C Windo	PAN 30 from 1948 Dustjacket Cover Artist Bruce C Windo
PAN 36 from 1948 Cover Artist Bruce C Windo	PAN 36 from 1948 Dustjacket Cover Artist Bruce C Windo	PAN 40 from 1948 Cover Artist ?	PAN 40 from 1948 Dustjacket Cover Artist Stein
PAN 44 from 1948 Cover Artist ?	PAN 44 from 1948 Dustjacket Cover Artist ?	PAN 48 from 1948 Cover Artist Bip Pares	PAN 48 from 1948 Dustjacket Cover Artist ?
PAN 68 from 1948 Cover Artist Lowess	PAN 68 from 1948 Dustjacket Cover Artist Val Biro	PAN 70 from 1948 Cover Artist Stein	PAN 70 from 1948 Dustjacket Cover Artist Sheila Sanford
PAN 72 from 1949 Cover Artist ?	PAN 72 from 1949 Dustjacket Cover Artist ?	PAN 73 from 1949 Cover Artist Bruce C Windo	PAN 73 from 1949 Dustjacket Cover Artist ?
PAN 74 from 1949 Cover Artist Stein	PAN 74 from 1949 Dustjacket Cover Artist F Porter	PAN 74 from 1949 Dustjacket Cover Artist F Porter
PAN 77 from 1949 Cover Artist Stein	PAN 77 from 1949 Dustjacket Cover Artist	PAN 79 from 1949 Cover artist Bruce	PAN 79 from 1949 Dustjacket Cover artist Sheila Sanford
PAN 80 from 1949 Cover Artist Bruce C Windo	PAN 80 from 1949 Dustjacket Cover Artist George Woodman	PAN 83 from 1949 Cover Artist Bruce C Windo	PAN 83 from 1949 Dustjacket Cover Artist
PAN 90 from 1949 Cover Artist Bruce C Windo	PAN 90 from 1949 Dustjacket Cover Artist Jack Matthew	PAN 90 from 1949 Dustjacket Cover Artist Jack Matthew
PAN 138 from 1950 Cover Artist Tansley	PAN 138 from 1950 Dustjacket Cover Artist Tansley
PAN X434 from 1965 Cover Artist After Raymond Hawkey	PAN X434 from 1966 Dustjaket Cover Artist Film Tie-In	PAN E5 from 1967 Cover Artist John Raynes	PAN 330400055 from 1969 Dustjacket Cover Artist Film Tie-in
PAN T45 from 1968 Cover Artist Glenn Steward	PAN 0330 300458 from 1969 Dustjacket Cover Artist Glenn Steard	PAN 0330 021052 from 1968 Cover Artist Douglas Ettridge	PAN 0330 021052 from 1969 Dustjacket Cover Artist Glenn Steward