Lillibet - as chris08226 says, we proofread every book that is member indexed and give a lot of feedback to member indexers to ensure the quality is as good as our professionally indexed books. However, we are not checking the recipes indexed against the actual book so if any member ever notices that a recipe is missing, please let us know and we will add it.
I agree that is unlikely that any member would choose just to partially index a book. If anyone wants to index only their personal favorites from a cookbook, they can do that as Personal recipes which are then only available in their own searches.