My numerous experience in PEY is Crew care as much as they bother to check, which they don't. Usually after meal time what they do is put out the tray table as a marker that this seat is open and unoccupied, but when they go back to rest they rare come back up. Then some people in Y would gladly move up and unfold the table and sit. Once a person just came and sat next to me which I politely told him to leave, but people are doing it.

There are even some Y that just went ahead to J if the last few rows were fairly empty, again, the crew doesn't seem to come around and check. Usually the get away with it till second meal time.