Generally if you have one single database install then checking the database inventory will give you the latest patch details. But! if we have multiple database in single oracle home then it might not give correct results. There might be a chance that one DB is applied with latest patches and others are not. In such cases, we need to check last CPU applied by logging into the database using below query:

Query to Check Last CPU Applied on a Database:

col VERSION for a15;
col COMMENTS for a50; 
col ACTION for a10; 
set lines 500;
select ACTION,VERSION,COMMENTS,BUNDLE_SERIES from registry$history;

What are Critical Patch Updates (CPUs)?

Critical Patch Updates are sets of patches containing fixes for security flaws in Oracle products. The Critical Patch Update program (CPU) was introduced in January 2005 to provide security fixes on a fixed, publicly available schedule to help customers lower their security management costs.