RELENG_5 branch exist?

[Sancho2k.net Lists]

I installed FreeBSD 5.0 expecting to be set to track a -stable branch 
for it. I assume this would be called RELENG_5, but I see the following 
branches exist with no RELENG_5:

RELENG_5_0
     The release branch for FreeBSD-5.0, used only for security 
advisories and other seriously critical fixes.

RELENG_4
     The line of development for FreeBSD-4.X, also known as FreeBSD-STABLE.

Is 5.0 not far enough along in development to require a -stable branch 
yet? What would be the difference between tracking 5.0 security and 5.0 
stable?

TIA

DS