Originally Posted by
Kisho
The game doesn't check if you've already got an item. It just gives you a random item from the boss' loot table, assuming you've gotten past the chance to win an item in the first place.
It also definitely does not check if you've entered a BG recently, or anything like that. It's simple:
-The game rolls to determine if you win loot. I believe this is a 15% chance, but I could be wrong.
-If you win loot, the game then rolls to determine what the loot is. As far as I know all loot is on an equal drop chance at this point, with the obvious exception of mounts. It also checks spec and choose a 'suitable' item (filter for your class/spec on the boss' loot table in the dungeon journal: if the item is there, you have a chance to win it)
That's it. No further checks made.