The current PTE, and all PTE's, are set up by the developers for their testing. If fixes are to be implemented, or changes, then they are tested first on the PTE and they get some feedback from the players. Often though it is the developers seeing data in logs about an issue that alerts them to the need for modifications. They can simulate a lot before it goes public on the PTE, but they don't have the ability to have 100-150 players playing at once and interacting.
I can't set up a server - and I doubt they will as this one only started yesterday. If they need to fix changes implemented in 19.1 (in their view) then in due course it will be rolled out to the PTE for testing.