Could just be luck, but I almost always get an event item drop.
I’m normally in a party of 10 people and several members of my party receive a drop.
Which boss are you referring to, and which event?
For the current High Seas thing, just find an orc or merchant ship and fire cannons at it until the ship stops moving. The cargo can drop in your pack sometimes, but the hold and crates on the dead ship always has some. Board the dead ship and loot the hold and various containers on the deck. We have also gotten pack drops from killing serpents and such, but have not found any on corpses. You take the cargo to an NPC at Buc's Den, near the mint, and he gives you points (doubloons) in a similar system as Halloween Treasures of X events. Instead of a 1:1 item:point ratio, however, the number of doubloons you earn varies by the quality and type of the cargo. Metal is worth more than cloth, legendary is worth more than grand master, etc. When you have enough doubloons (points) you can buy items from the same NPC. The beacons have higher level cargo drops which reward more points. The Devs have said they will add a new item on the NPC each month that this event is active.
Alternatively, you can deliver the plundered trade cargo to the city it was intended for. That city gets a nice gold boost for its treasury. You can also take the cargo to ANY city's minister of trade, but that city only gets half of the gold as the proper city would have.
For event bosses like the Khaldun champ or EM bosses - most bosses have pretty high fame. You will likely get a fame notification in your journal upon its death if you have earned loot rights. Those bosses typically have pack drops for the rare items. There are exceptions but a boss generally only offers a limited number of drops, so if 50 people are attacking it... well, not everyone gets a drop.
thank you everyone for leaving a comment, I have a better understanding now of where i am lacking in the mechanics. thanks again meow