In looking through a variety of Paradigm For Sale ads it appears that specific models have a range of varients.

It appears that Paradigm distinguishes this by adding a v.X after the primary model number.

Anybody have any knowledge of what is going on?
Sure. Each updated model is designated with a new Version number. That way you can tell the vintage.

What line are you looking at? The current/latest versions of each line are as follows-
Monitor V.5
Studio/Reference V.4
Signature V.2
How do the versions relate to year of production?

What changes were made with the version changes?

do your own google search my friend! unless someone has been a long time Paradigm dealer or owned each individual speaker as it has been updated, it is unlikely that anyone would know he differences between versions without doing a google search themselves.