I believe what you're asking is:
- Is the loot randomly generated at the moment the creature is killed, therefore, it MAY depend on the moment you killed it, and WHO killed it
- Is the loot for every creature predefined when they respawn, so it wouldn't matter who killed it, the loot is the loot and won't change. Example: That Yeti WILL loot the bunnyslippers whether you or me killed it, whether we killed it now or in 2 hours.
If we take into consideration the fact that loot has PARTICIPATION LEVELS AND THRESHOLD, then it HAS to be the 1st option. If loot was predefined, then participation levels would not matter and anyone would be able to loot anything.
Now, assuming the 1st option is the correct one, HOW the loot is generated, how they apply the % chances, etc.. that must be a very complex formula which I'm afraid we will never know for sure.