Frequently in SAO, players discuss how loot, items, and money will be dispensed when grouping or teaming up.
In MMOs that I've played, loot is divvied up by the system to each player based on what they kill. When you get to a high enough level to get magic items, then there are methods for each player to lay claim to the item, and the system determines who gets it.
In SAO it clearly must be different. In season 2 episode 21, this comes up with Asuna and the Sleeping Knights, when they forgot to give her her share of the loot from killing the boss.
The system has no way to know who was an original member of the party; does that mean that the party leader gets all of the loot and then distributes it?