I have read the RedHat errata about the patching to fix the
potentially exploitable vulnerability

It stated that before applying this update, make sure all previously
released errata relevant to my system have been applied.

Does it mean that if I were going to apply the latest DNS patch, I
would have to first patch all the OS patches and all the previously
released DNS fixes? If it is so, how do I ensure all the previously
released patches have been applied? Is there a way to check it?

Will the system prompt for any error, if I haven't installed enough
the earliest patches?

Please enlighten me. Thanks.