Please read.
You ask about TH+ 8.
The dev said, and I quote:
TH is essentially a debuff.when the value of Treasure Hunter placed on a monster and the value of the Treasure Hunter on your character are different, this will cause the growth rate to vary.
When you use TH+8 total, and then proceed to proc to 9, and you remain in only TH+8 total, there is now a difference between your TH value and the enemies TH value.
This will cause the rate to now vary. As there is now a difference between your value, and the enemies value.
If you then proc to 10, and you continue to remain in TH+8 value, there is an even larger difference between your equipment/totals and the enemies total.
This means you encounter a decay, or a loss in your proc rate.
If I am in TH+14, and I proc from 8 to 9, there is no "loss" in difference. As stated by the Developer:
So clearly it is being said, that using any TH+ total value below the current enemies value, will not "increase" the rate, but will instead "lower" the rate if your value is lower.Adding Treasure Hunter+ via equipment, or other means, will not increase the rate at which the Treasure Hunter value grows, as this is a set rate.
This is a source directly from the developer, clearly stating, that using anything below TH+14 when trying to proc to TH+14 will cause a reduced chance.
Using only TH+8 while trying to proc to TH+10 from TH+9, which:
In other words, it is "important" to use TH+ equipment, removing the need for TH+ equipment,results in an inefficient means for increasing the TH value.
Thus, they have no plans to change how TH+ equipment affects the system as a whole.takes away all the hard work some players have put into maximize their Treasure Hunter.
There is your source, that using anything lower than TH+14 will reduce your chances to proc to a total of TH+14 on the enemy.
If you are using only TH+8, trying to proc to 9, 10, any number past 8 will be reduced. As stated by the developer. The source you quoted is the source that says this very information.