--Author Unattributed for His/Her Protection
I was surprised (and, I admit, I laughed and laughed) by the error here caused by trouble with spelling similar-sounding words. The writer meant to indicate that the books were eligible.
Both of these words are Latinate, and perhaps therefore inherently confusing.
Eligible is an adjective meaning that the noun is able to be elected or selected.
Illegible is an adjective meaning that the text in question cannot be read for any number of reasons.
It's important to distinguish between e and i sounds, and to intervene with a critical eye when SpellCheck messes with them, or else a book that readers can choose may become unreadable. There is no worse fate for any book!