Completeness of Patch Population

I'm performing an audit on Oracle database changes and the database is on a Linux OS. After using the command **opatch lsinventory**, we learned that this command has not been pulling the complete population of patches on the database. It is only showing the last patch applied. Contrary to many online definition; which is ALL patches. What could be causing this? What's a foolproof way to pull all changes (patch, scheme, table etc) applied? Thank you all!