Someone please explain the concept of DT3 for me. Does it exist?
DT3 is a user on DT2's trust list. They have no power because in general only DT1 and DT2 have power and by default the depth of trust is 2. They can be called ordinary users, but not members of DT2 who are already on DT1's untrusted list. Correct me if I'm wrong.
Try reading the description in the thread you quoted:
The list of the DT2 group is based on the current overall trust from DT1 members.
If one DT1 member adds an ordinary user to his trust list, that user gains +1 score and becomes a DT2 member. If this DT1 member subsequently excludes him from the trust list, that DT2 member becomes an ordinary user again. If another DT1 member using the "~" character adds a DT2 member to his distrusted list, that user gets -1 score but remains in the DT2 group with a zero rating. If yet another DT1 member adds this DT2 member to his distrusted list, that user leaves the DT2 group and becomes an ordinary user again. In this case he cannot be included in the list of DT3 and further. By default the trust depth is 2, therefore ordinary users do not trust the opinions of the members of DT3 and deeper.
Since user trust in each other is always changing, I decided to create the TOP-200 of the most trusted users in the groups DT1, DT2 and even DT3.