PCLOS is a rolling release.
Decisions have been taken at intervals - about every 3 years - to require a reinstall.
Those decisions were taken to eliminate the likelyhood of users breaking their system if something went amiss with some very basic underlying stuff being updated.
As I understand it, the devs would have updated on a rolling release, estimated the possibilities of such updates causing hassle, and taken the decision that the course of least upset for the majority of users was a reinstall. I guess we cannot all be devs, and it seems PCLOS does not expect us to be.
Some indication of the problems became visible during an update from 2007 to 2009 (I think) where a lot of users had problems they were unable to sort out, and just reinstalled anyway. Others had no problems and some more had problems which were sorted.
All of that took up way to much time and effort in support on the forum, for the benefits gained.
I believe the decision for staged reinstalls was influenced by that experience.
I first installed PCLOS as my main OS in 2005, having played with it and other distros for some time.
In 2007 a reinstall was deemed necessary, and again in 2010.
In between the updates were on a rolling basis.
So I guess in one way PCLOS is not a "true" rolling release, in that it has required a reinstall twice.
On the other hand it seems to have come to a very pragmatic and workable means of having a rolling release in between major reinstalls, which have happened only twice to date. This appears to be for the benefit of users.
Heck there were distros that did not last as long as a PCLOS install and rolling update
To me it is a rolling release. Others can call it whatever they wish ... it hardly matters.
The scheme works, and works well for users, which is the main thing IMO.