I can not answer all of this.
But in general they support the versions a long time. And when they stop they write like this:http://liste.pardus.org.tr/pardus-announce/2011-September/000104.html
I dont know if it be a Pardus 2011.3 or a Pardus 2012.
This can be a help to:http://en.wikipedia.org/wiki/Pardus_(operating_system)#Release_history
I prefeer a fresh install only if it's a new line.
You could describe the 2011.1 and 2011.2 as a sort of service pack 1 and 2 for the 2011 version.
Not necessary to do a new installation, just do the normal update process.
But when it be 2012 it's a major change.
If you see it was never a Pardus 2010 because they support the 2009 version a long time.
So it's not necessary with special LTS versions as Ubuntu for example.
This is a good source for information if you use Google translate:http://www.ozgurlukicin.com/
I think it a well balanced process. Stabile but not to old versions. A good compromise that works fine.