This series of four 8 vo. books was published between 1915 and 1933. Book #4 Little Black Sambo was only published in 1931 in one format (Format 4).
The other three books:
1. The Tale of Peter Rabbit
2. Three Little Pigs
3. The Little Small Red Hen

were published in three different formats. All originally had dust jackets which are fairly hard to find.

Here are examples of each format:
Format 1- Line drawn illustration on the front cover.

Format 2- Front cover appliqué has a book appropriate color illustration. The cover illustration is a duplicate of an internal picture.
This book says Printed in the United of America on the title page. This indicates a post-1922 publication.

Format 3- This format has a full cover pictorial color appliqué which is not a duplicate of an internal picture.
This book says Printed in the United of America on the title page. This indicates a post-1922 publication.

For more on this series see: Juvenile Quartos