I apologise for the misleading information, which came from an early and now incorrect promotional website.
Sandwiched between the 1950s and the 1970s, here are the 1960s, Penguin Decades style.
These ought to pop out on the shelves like jars of sweets. I especially like the cover for A Clockwork Orange, which fits the book beautifully while getting away from the stylised portraits of Alex that are often used. Speaking of which, I found an earlier sketch for that cover, showing a direction Aldridge decided not to pursue.
I just have the 1980s books to display now, with covers by John Squire. I have tracked down three of the five covers, so I hope to post them soon.