Indexes are finding aids to take the researcher to the actual record. They are not mean to replace the actual record. Indexers can make mistakes by transcribing names incorrectly or leaving names out.
Do not rely entirely on an index to a record to find what is in it. Search manually if you have reason to believe that a person who does not appear in the index should be in the actual record.
Do not rely on the index’s transcription of the record to be either complete or accurate. Look at the record yourself.