The VX3 came out Feb 2004 and superceded the Vari x 3 side wheel which came out in 1997.
Not sure of the mechanical differences but they did change the threads to metric.
Theres also many different variations of the Vari X 3's, mostly non side wheel 25mm and 30mm tubes, 40 and 50 front bells in any combination.
The last of the PR modded by the master himself would be June 2005, he had a heart op in early August and died in the October. I probably had the last one ever done, **** sounded very very rough in May that year.
I know of three PR VX3 Jan 2006 done by his son Chris, all with standard rets.
Since its a production scope they will vary from one to the next, thats why there are differences.
Every one i know who has had a VX3 hasnt reported any shift unlike some of the Vari X 3.