story
Previously, CentOS was a rebuild of RHEL. In between RHEL releases, CentOS was exactly the same as RHEL. When RHEL had a release/fix/backpoint, CentOS trailed until it was rebuilt from the new RHEL source.
The "old" CentOS was exactly the same nearly always (nearly perfect overlap) and the "new" CentOS is exactly the same nearly never (almost no overlap).