What is the goal of the ports quarterly branches?

[Mel Pilgrim]

I have ports/branches/2015Q4 checked out for poudrerie thinking that it 
would be aligned to what's in the quarterly pkg.freebsd.org repos, but 
that doesn't seem to be the case.  For example, right now 
pkg.freebsd.org has dovecot2-2.2.19, but the 2015Q4 branch only has 
dovecot2-2.2.18.

I thought (one of) the goal(s) of the ports quarterly branches was that 
the pkg.freebsd.org quarterly repos would use them, thus making life 
easier for those of us who have to build at least some of our packages 
from ports?