Still can't find any ATSB reference to the "part of an oxygen cylinder and valve (which) entered the passenger cabin and impacted the number 2 right door frame handle" having been found. So has it?
As I understand, the hole in the cabin floor is (almost) directly above the hole in the fuselage wall.
Various items were reported as being sucked across the cabin by the depressurisation, and any debris that 'came up' could realistically have fallen and gone down and flown out of the big hole to the outside world.
After all, some of the hold cargo ended up jammed in the hold, so it is reasonable to assume that other material might have preceded it . . .