And that base/version mecanism is what make rF2 able to keep multiple versions with their base.
Imagine an item with 4 versions installed.
1.01, 2.05, 2.07, 3.01
In game (single) you will only see the "last" 3.01 but if a server uses other versions it will work perfectly and you will be able to connect.
In Installed folder you will have folders :
1.00, 1.01, 2.04, 2.05, 2.06, 2.07, 3.00, 3.01.
At some point previously rF2 was able to keep older versions based on "residual" vmods and never uninstall them if the vmod was kept. Again pure facts seen by experience in older versions ...