This has maybe only an indirect relevance to the question, but there is a Jain text, Paesi-kahanayam, which has many similarities with the Payasi-sutta (DN 23). This is a debate on the soul, and it is one of the most entertaining texts in the DN. The text of the Buddhist sutta is a dialogue between the Buddhist monk, Kumara-Kassapa, and governor Payasi. The commentary says it took place some time after the death of the Buddha. One interesting point is that Indian names often have a meaning. In Pali the name Payasi has no clear meaning. But in the Jain text the same person is called Paesi. In Ardha-Magadhi, the language of the Jain text, the name Paesi can easily be seen as Sanskrit Pradeshin, which means "District Governor" - which is what Paesi/Payasi was. Therefore the story may originally be a Jain story, written in Ardha-Magadhi. Some Buddhist editor then may have borrowed the story, making some changes to make it Buddhist, and just transferred the name Paesi into Pali > Payasi. If the original had been in Pali, we might have expected the name to be Pradeshin > Padesi. Therefore, this text may be evidence of borrowing and cross-influences between the different religious schools in ancient India.
As mentioned, the Payasi-sutta is an entertaining text with many interesting parables. In the debate the Buddhist monk argues strongly in favor of the existence of a soul (and of course he wins the debate), and this may also be an indication to an 'external', non-Buddhist, origin of the sutta.