The books you can see in the gallery on the left are something of the 606d 'missing link'. In 1979 Ladybird re-launched and re-packaged the 606d series after a gap of 5 years in which no new titles were published. The repackaging involved presenting them in a standardised light green cover, with a 'lozenge' decoration on the front cover and breaking away from the traditional Ladybird format of presenting a full page of text on the left and a full page illustration on the right. A wide range of different artists were called upon to illustrate the new titles and to re-illustrate completely the stories originally produced by Eric Winter/Robert Lumley.
However, for some reason, some titles escaped the re-illustration for quite a few years and, although they were packaged up with the same cover design as the other books, the contents remained unchanged from the earlier versions. The reprieve was termporary. Eventually every book from the original 27 606d series except for two ('Puss in Boots' and 'The Old Woman and her Pig') was given a 1980s-style makeover.
As a result, for a few titles you can find two different books in the green-cover, later 606d version. If, for example, you fondly remember 'The Three Little Pigs' from 1965, don't be put off by the cover design of some later style books with that date in the front; once you turn the page, you will be back into the book you once knew so well. On the other hand, the very 'cartoony' style illustrations of the 1989 version would be as uninviting as a big bad wolf coming down the chimney.
The pictures on the left show the two cover styles. There should be another couple of books in this gallery: The Sly Fox and the Little Red Hen and The Three Billy Goats Gruff also exist in the two different versions, but I couldn't find copies when I took the photos.