Since many of you asked, I'd better put these into instructions for you to follow. It is possible to put as many notebooks into the leather cover as you want, that is if you can tolerate a thick pile of paper.
First, the elastic band which came with the notebook is already configured in a way you can put 2 notebooks in the cover.
To add 2 more, simply use the additional elastic band to hold Notebook 3 and 4 together in their spines.
Then insert this Notebook 3 and 4 duo underneath the first two notebooks, i.e. between the cover and Notebook 1 and 2.
Finally, pull Notebook 3 and 4 through so that all notebooks' spines are met. Hope this helps!
