About 72% of my books are indexed. I have a lot of older books, mostly Canadian authors, that are not indexed. Although many of these books were once very popular, they are now not owned by enough members to merit indexing. This is too bad since they remain some of my favourites. I have indexed a few myself, and will continue to from time to time.
I sometimes write a note for an unindexed book noting some of the recipes I've made since this might be helpful to others.