The Roman numeral versions were discontinued years ago and replaced with the VX-1, VX-2, and VX-3, which were also discontinued 2-3 years ago. The VX1 and VX2 were dropped and replaced with the VX-Freedom. The updated VX3 is now the VX3i. And even older were the Vari-X I, Vari-X-II and Vari-X-III.
Over the years Leupold has upgraded and WHEN some of them were made matters. A VX2 made 2012 or newer is a better scope than a VX3 made in 2011 or older. All of the versions with Arabic numbers are better than the Roman numeral versions. The difference was mostly in the glass quality. All of them were pretty tough. Many older lower end scopes used friction adjustment while the better ones were click adjustable. All have been click adjustable since 2012.
The older VX-1 was a big step down from the VX-2, but the difference between VX2 and VX3 was much smaller. The biggest difference is that the VX-3 could be had with options for different reticles and other options not available on the others.
When Leupold went from the Vari-X to VX designation there was an upgrade. Same as when they went from Roman to Arabic numbers. But in 2012 they also made major upgrades with no name changes. The new VX-1 was essentially an older VX-2. New VX-2's were essentially old model VX-3's and the VX-3 was also improved, but there was no price increase.
The new VX-Freedom is supposedly the old VX-2, with minor cosmetic changes and priced at the same price point as the old VX1. But I've not used one so I can't say for sure. I do like the newest versions of the VX-2. For my money it wasn't worth the extra cost to go up to VX-3.
If I were buying used I'd pass on the Vari-X versions as well as one of the older Roman numeral versions. They were good in their day, but there are better options today. Plus many of those scopes are 30+ years old by now. I don't trust the rubber seals in optics that old.