I don't think the title is gramatically correct but I dont care.

So we released 4 new versions that runs in your web.
Versions:
2012
2013
2014
2015
We still use the 2016 source code for the main engine, the versions are just skins since we do not have the source code for these versions (might change later butyeah)

We thank aya for the source code of the corescripts and the switching.

For scorpion developers, we are honoured to include new APIs that allow for a better user experience which is an API that would allow changing the versions in real time. Here is how to use it:

The method to use is "StarterPlayer:SetVirtualVersion(year)" the argument is that the year is what year, you should use 2012, 2013, 2014, 2015, 2016. we dont know what happens if you set the year to 2021 (nothing).

BUT YOU MUST SELECT THE GAME TO "Game Select" or it wont select.

StarterPlayer:GetVirtualVersion() returns the current year, great for debugging if needed.

StarterPlayer:IsVirtualVersionLocked() returns true or false, great for debugging if needed. you should select "Game Select" so its not locked.

How would you use it?
local StarterPlayer = game:GetService("StarterPlayer")

if not StarterPlayer:IsVirtualVersionLocked() then
local ok, err = pcall(function()
StarterPlayer:SetVirtualVersion(2012)
end)
if not ok then warn(err) end
end

this can be used to improve the user's experience, i have tested it and it works so you should try to check it out. but bugs are common so your feedback helps.