Source:
viewtopic.php?f=2&t=25584&start=120
Original text(JP):
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Kumasuke??
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pei??
?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ?????????????????????????????????????????????????? ??????????????????????????????????????HP?????????? ???????????
And then, this is Elmer's translation.

Originally Posted by
Elmer the Pointy
When there are multiple instances of Treasure Hunter in a party, the strongest effect is used. Treasure Hunter goes into effect the moment the Thief actively puts their self on the target's hate list. For the most part, once the Thief attacks a monster, they remember the effect of Treasure Hunter. If a Thief dies, they do not have to be Raised to strike the monster once again. However, if you lose possession of the monster and they regenerate back to full health, this information is lost.
In any case,

Originally Posted by
Shamaya
-Is TH cumulative? ; That is, does 2+ thf in different parties in an alliance(s) = improved drop-rate.
This question was actually asked in the Q&A that day, I don't know why Elmer missed it in his translation, anyway, their answer was: When there are multiple players with the Treasure Hunter trait, only the strongest effect will be active, the additional Treasure Hunter will not be added to the effect.

Originally Posted by
Shamaya
-Does the party with the thief need to get the kill?
I would say from what Elmer translated and the original text that the effect is like a debuff that you put on the enemy, with that in mind, it probably was pretty obvious that THF only has to "put" the treasure hunter on the target to trigger its effect.
What I am more interested in is really the last point of yours: whether or not I can switch back to a better dagger and hands(when I get my armlets...) after the TH effect is placed. Is TH like a debuff(think "Slow" "Paralyze")? And does the THF need to be actively be on TH2+2 to keep the effect at TH2+2, if +2 equips are removed, will it become TH2 only?
Lastly, what is the general belief of "Getting on the hatelist"? I would say any action that causes an enmity increase would activate TH, however, according to the last few posts on the
Treasure Hunter thread, only an offensive action that is performed onto the target will activate TH; the problem is, it wasn't fully tested, with lots of assumptions as well.