Your inquiry might become visible to more people able to help if you use the Simple Touch forum. This forum is frequented by people that own the original Nook model with is now referred to as the "First Edition". Try clicking the Browse Book Clubs link above and looking for the link to Nook Simple Touch Support or click http://bookclubs.barnesandnoble.com/t5/NOOK-Simple-Touch-General/bd-p/STGenDiscuss
Check the sizes of your books and compare the total to the capacity of that memory partition on your Nook. Some books are significantly smaller than a megabyte and the total size of your purchases might not total a full percent yet. This is where the Simple Touch forums become useful, since they would be more familiar with determining eBook file sizes using the Simple Touch reader itself. You could also access your account with a web browser on a computer and read details about your purchases there.
There may also be issues related to ePublications downloaded from other sources being stored in a different 'disk" partition on your Nook than the partition where eBooks and other material purchased from B&N are stored (might be a hidden partition on the Simple Touch).
I recommend installing a software reader on a desktop or laptop computer and using the facilities in the software reader (not the "Download" button accessing your B&N purchases with a web browser) to download the ePublications you purchase from B&N. Once on you computer you will be able to use the data backup procedures you use for that device to preserve your purchases on a removable device like an external hard drive or flash drive.
