Index help for a newbie

Hi!  InDesign newbie here.  I have been tasked with trying to create an index for a book with 7 seperate files.  I have all files loaded into one book file, and the index works pretty good for the most part.  However, I have figured out that for some reason, it's not picking up all the entries.  For example: this is a book with around 150 names of people in it.  I have set the index up for each person's name...but after doing a spot check, I notice it's only showing some of the pages where these names are, not all of them.  Like...Joe Smith I know is on at least 10 pages, but the index is only showing he's on 3.  Any ideas of what might be wrong?  Or do I have something set up wrong in the files I wonder?  I'm so frustrated!