When using any index, determine what that index covers and what it does not. Most census indexes are every name indexes, but many other indexes are not indexes to every name contained in the record.
Death certificates contain many names, but indexes may only index the name of the person who died.
Probate indexes often only index the name of the person whose estate is being settled. Names of beneficiaries, witnesses, debtors, lenders, etc. are often not indexed.
Deed indexes frequently index only the name of the first grantor and the first grantee. Other grantors and grantees are not included and names of neighbors listed in metes and bounds descriptions to property are not included.
When using any index to any record, determine what names got in the index and what names did not.
And…understand who potentially could be mentioned in a record of the type you are using–that helps you to search as well.