Jainism: History (Wikipedia)
Parshvanatha, the twenty-third Tirthankar, is the earliest Jain leader who can be reliably dated. According to scholars, he probably lived in the 9th Century BCE
The statement above may be an indirect clue to our puzzle: if the 23rd tirthankar lived three centuries before Mahavir, and if this kind of separation in time characterizes the whole sequence of Jain ‘jinas’, then that puts the origins back very early indeed.
Well before the IE entry (assuming the AIT).