Where is the carpet dupe actually still possible?
To my knowledge, on all servers that run on 1.12 and have no plugin installed against it. Large servers will not be affected.
Why do you really want a server where you can exploit such a bug?
I read it from 1.8.9, definitely at 1.13 because it was abused in Craft Attack.
As of 1.8.9, that definitely wasn't possible. This bug is based on the quick update of observers that were only added in 1.11.
Unfortunately I didn't see CraftAttack, but they probably didn't have a plugin installed against it - large servers did. As far as I know, this was definitely fixed in 1.14, just look for a slightly smaller 1.12 / 1.13 server.
