I hunted a boss down in S2, just when i picked up the drops, the server got dced and was rolled back few mins. When i relogged i see the same boss (it cant respawn so fast) and i killed it again, however with diff drops. So it can be said that drops are randomly allocated to monsters.
However on a larger scale its possible on server side to give a menu of drops from which the drops would be finally chosen, like indian server bosses r made to drop ... well nothing
