Did the other true souls get 'their' tadpoles by being abducted or did they bargain and volunteer?
The introduction of the Absolute is bizarre. The openin montage implicates days, not months or years. Yet the Absolute is an established religion with armies, leaders, religious ceremonies. Its a thing. The True Souls, even if "new", wouldn't be as new as you to be in the positions they are. Even festering in secrecy in the wilds, it just doesn't seem like it could have grown this quickly. So, odd that its been under the radar this hard. Lets just go off the assumption that, regardless of time, its somehow well established and True Souls are party of their DNA. That has to mean that an illithid hub exists somewhere (moontowers?) that is controlling things to this extend and providing slugs. The dude you meet in the underdark "left" and is hanging out in an area that uses mind control techniques beyond those that are psionic driven.
If this ultimately leads to a mind flayer colony and an elder brain or something, theres a lot more things they could offer that would tempt someone into their reaches than the hokey religion of some garbage eating goblin brands. Its a cult, it has a leader, wheres the recruitment process? I wont drink a drop of the kool-aid until I have my black nikes damnit. I want to be convinced.