[CentOS] CentOS-7 Security Updates

Hi all,

I'm trying to clarify the security updates policy for older CentOS-7
releases.

There is a number of servers I'm supporting that are running CentOS-7 1503.
When 1511 was released several days ago I've tried to upgrade several of
those, but failed. I've got some strange errors with e1000 virtual NIC
being restarted frequently with 'tx unit hang' errors. Anyway, it's not the
thing I'd like to discuss here.

What I'd like to know is the answer to the question "will there be any
security updates for CentOS-7 1503, and how long"? I was searching on a
wiki, but couldn't find anything clear enough. What I've found is the
phrase in 1511 announcement letter

  This release supersedes all previously released content for CentOS
  Linux 7, and therefore we highly encourage all users to upgrade their
  machines. Information on different upgrade strategies and how to
  handle stale content is included in the Release Notes.

This makes me think that there will be no security updates for 1503 and the
only way to get them is to upgrade to 1511, but I'd like to find any proof.
Unfortunately, there is nothing about this in Release Notes :(

-- 
Regards,
Dmitry Teselkin