So I did a world boss, one at yorn and the other at shushire, both around 50-80% left on HP when i joined the raid.
I automatically received the quest but upon completion, I didnt get credit for the kill in the adventure tome. I also didn’t get any opportunity to roll on any items dropped.
You need to be a certain item level to deal damage, and thus receive credit. If all 100% of your attacks are being “Blocked” you dealt 0 damage and did not participate in the fight. Come back later when you’re higher item level.
You need to be x ilvl in order to deal damage, and to get it counted you need deal at least 1% of total damage, also then you get to join auctioning drops
Edit: If you check field boss on event schedule it shows the minimum ilvl you need to participate
Field Boss: Spawns every hour on certain day(s) of each week, can kill X amount of times but you can only get ONE Per Day it spawns. Has minimum ilvl requirement
World Boss: Spawns every day of the week on a 30 minute or longer respawning timer (i.e. Castrick of Balakar Mountains is on 2 hours), can kill x amount of times.
You can get the rewards once for bosses that spawna ccording to compass schedule, but you get the adventurer’s tome reward even if you kill them when you already obtained the rewards.
As for the drops, I did Moake that has 1415 recommended level at 1340, been doing him every day he spawns since. Got 2 pieces of legendary 1370 armor equipped even though I’m 1355 only.