I think it can be logically inferred that they had unknown founders. Are you asserting that these religions would have existed in the absence of humans?No, I mea they have no founders and are usually descended of folk traditions. Egyptian, Greek, Sumerian, Arabian etc. religions have no founders. Many polytheistic religions have not.
If not then even if the changes in religion were small enough over time that it was more like the development of language each person in the chain who introduced some small change was a partial founder in what would come to be identifiably different from the parent tradition over time.
In my opinion.