Later on it says:
It depends on how they coded it. If they re-used an old system and just gave it updated tool-tips they may not be able to change it without patching all those items over. Like the reason you can’t add a gouged eye socket to an already socketed item – the code that sockets the item shares the same ID space as the gouged eye would add.
If Blizzard made the code for corruptions completely new for 8.3, then they should be able to find a way to re-corrupt items that have been flagged as cleansed.