Copperbell Hard for int book 2 on stardust rod, killed the target no update

[Gwaeron]

[...] the fact that you don't have to actually kill anything to get an Atma from a FATE is just an anti-frustration feature meant to allow Atma acquisition from any FATE in an area. Seriously... imagine how bad the backlash would be if the chance to get an Atma wasn't based on just completing a FATE, but rather on your ability to tag mobs.

Additionally, since we're stabbing at lore here: If they're "one of a kind" enemies, why can we kill them repeatedly?

You're just proving my point here. The book not "knowing" you killed an enemy just because you were alive makes no more or less sense than many other story-related things. I don't even know how many times I've defeated Gaius by now. So why then does "lore correctness" in this particular matter make sense, even at the expense of a major inconvenience?

I've heard from more than one source that it won't count unless you are alive in the boss arena. If you accept the "Revive at dungeon entrance," you won't get credit for the kill.

False, you do get credit for the kill as long as you are in the dungeon and alive. Tested and confirmed.

[Donjo]

You're just proving my point here. The book not "knowing" you killed an enemy just because you were alive makes no more or less sense than many other story-related things. I don't even know how many times I've defeated Gaius by now. So why then does "lore correctness" in this particular matter make sense, even at the expense of a major inconvenience?

There is this concept called "Gameplay and Story Segregation"(credit to tv tropes for the name). It basically means that sometimes, what makes sense in lore/story does not make sense in gameplay terms, or vice versa. This is usually done because it's a game and aligning story and gameplay in some cases just makes it less fun or in itself just doesn't make sense. An example of this we've identified is that it makes no sense that 100 different people can kill the same "one of a kind enemy". However, it makes sense in gameplay that everybody should be able to challenge it. It doesn't make sense in lore that you can get the "crystallized essence of a fallen enemy" for picking boxes up off the ground, but it makes sense in gameplay that any FATE can give it to you.

However, it's different in the case of you not getting credit for a boss kill if you're dead. In this case, story and gameplay are not segregated, but instead integrated. If you're dead when a boss dies, you didn't kill it. Everyone else in the party did. Why should you get credit for a fight you didn't survive? This is properly reflected in gameplay by not giving you the kill. This is not a "major" inconvenience. So you have to take another half hour or so to get to the boss again? That's not major. You go in, get some more loot, some gil, and some tomes on the way. Just be glad that you don't get locked out of loot for the same reason. It does, however, make no sense that you can be standing outside the arena and still get credit. That's silly.

I guess the point here is that just because X makes sense in both lore and gameplay doesn't mean that Y should too. It's up to SE whether or not to segregate them or integrate them.

[Schaeffa]

False, you do get credit for the kill as long as you are in the dungeon and alive. Tested and confirmed.

Then I stand corrected. I saw some people on Reddit talking about it, but I should learn to take Reddit posts with a grain of salt.
That being said, I wonder why people don't just revive themselves to the entrance of the dungeon right before the boss dies if it looks like the healer won't be reviving. Seems like this should be a non-issue.