What's in a (CentOS) version number?

I used to work for a certain fortune 100 company that had accumulated a mix of SLES and RHEL servers. SuSE was quite happy to support not only SLES but also RHEL, much more cheaply than Red Hat. We managed all of our Linux servers via the SuSE SMT (subscription management too) server.

I did notice that once you registered the RHEL servers with the SMT, it changed some packages including /etc/redhat-release, but as far as we could tell the OS worked just like the officially supported RHEL.