I have managed to acquire six of the Saalfield boxed sets. Other sets exist; I only purchase the sets for the series that I collect. All of my sets contain either the Adventures Girls or Linda Carlton books.
The following pictures show all of my sets together from the front, right, back, and left.
I am not sure of exactly when these sets were issued, but I assume that they are from around 1940. The boxed sets are very difficult to find, since most of the boxes would have been thrown away decades ago.