The 1913 Baseball Series Notebooks cards were those printed onto children’s notebooks. The cards on the notebooks were replicas of E95 and E96 baseball cards distributed by the Philadelphia Caramel Company.
While the same images and players from those sets were used, there are two main differences between these cards and the regular E95 and E96s.
First, the covers these cards were printed on are of relatively thin stock and noticeably thinner stock than the Philadelphia Caramel cards. Second, the cards had blank backs as the reverse was simply the inside of the notebook.
The blank backs can sometimes confuse collectors. They can be sold as proofs or prototypes but there have not been any true proofs from these two sets. E95 and E96 cards with blank backs are almost certainly from the notebooks. That is especially true if the cards are printed on thinner cardboard.
20 different cards are often listed as comprising the checklist. However, SGC has graded a total of 29 of them. If all of the notebook covers each contain five cards, that would mean at least one additional card belongs on the checklist.