Everyone in the thread has the correct idea with regards to the era switching idea.
The variant switcher (not to be confused with the era switcher) is merely being implemented to save on load times and menu listings of vehicles. I don't want to implement so many unit.xmls to the point that it will double the initial loading time. The variant switcher solves that problem. This is something that will be implemented due to people's criticisms of there not being a callable unit for the 1996 Caprice Slicktop, among many others.
For the 80s and 90s switcher, I have decided to go with a vehicle spawner, just like in multiplayer. Instead of wasting the players' time in having to manually spawn in each unit, I will give them the option to spawn in an 80s or 90s loadout, and then it is up to them to mix and match depending on what they want.
That way, if you want purely 80s, that choice is there, purely 90s is there too, and a mix/blended set to say, represent the late 80s or early 90s, you can manually call in units.
I hope everyone will feel satisfied by this arrangement.