Titan.Eiryn said:
From my understanding and SE's explanation of TH and the new "levels" you get from this update it works as such:
TH itself is simply an extra slot where a /random takes place.
TH1 = 1 extra slot
TH2 = 2 extra slots and so on
Use a wild rabbit as an example. A normal wild rabbit can drop Hare meat, Rabbit hide, a crystal or nothing. That is 4 items that are placed in the /random for each slot. Normally the rabbit only has 1 or 2 slots that it can drop one of these items in. Treasure Hunter increases the amount of slots that the items can be /randomed in. So a thf with TH5 would give the loot pool 6 or 7 slots that could drop one of those 4 items. You may not see 6 or 7 items drop because one of the items in the /random is nothing.
The new "levels" of TH do not give an extra slot for an item to drop into, they increase the % of the TH slots to drop something.
So say Hare meat drops at 15% chance, Rabbit hide drops at 15% chance, crystal drops at 20% chance and nothing drops at 50% chance per slot.
Based on the above example, here is my theory on what the "levels" of TH do. They increase the % on the item's chances of dropping per slot. So instead of 15%/15%/20% and 50%nothing, with highest tier it would be 20%/20%/25% and 35%nothing.
So to sum it up it isn't TH10 or whatever, its TH7 + 3 or 4 enhancement. Basically TH and the tiers that you are getting are not the same thing.
*edited*Feel free to correct me if I am wrong with some facts or announcements from SE that I may have missed about TH. My theory on the melee/SA/TA enhancements is open for debate though.
A while back SE stated that crystals have absolutely no weight in the treasure pool, and an item will always take a crystal's spot. Also, there is someone doing testing on BG. He removes different gear with +1 TH, and uses different characters with different levels of the job trait, and each one gives a +1 to TH.
Basically, if he started with TH+3 total at level 90 THF, his triggering TH attack would bring it to 4. If he started with a character that only had TH2, his triggering attack would bring it to 3. If he started with a character that had TH3 as well as thief knife, his triggering attack would bring it to 5. Therefore, each individual trait, and each individual bonus via gear/atma what have you is simply a single increase in Treasure Hunter.
Lawyered.
Edit - In regards to your idea about it opening up an additional slot, there are a few trains of though. Use Mee Deggi the Punisher for example. He has a single slot to drop an item, either impact knuckles or Ochimusha's Kote. Some think that stacking TH has no effect on him because it is either one or the other, and the game cannot determine which item you actually WANT, therefore it just causes it to random between the two. SE would have had to actually implement a mechanic on specific NMs where one item is weighted higher than the other outside of crystals (which will never replace an item) in order to achieve this. While possible, it is highly unlikely. In my opinion, I feel that TH simply increases the % chance that an item will drop. They set parameters for the NM, how many items it CAN drop, and then the system randoms on all the items in its possible treasure pool. If they succeed, the item will drop and fill up a spot. If there is only one spot, then the item with the higher roll will take that spot.