On Wikipedia, it seems to date Jarasandha, his son, and the Kurukshetra battle in and around 1500-1000 BC by citing Puranic references. How might this square with a 3500 BC date? I believe the Mahabharata cites astronomical information that secures the 3500 BC dating. How then does the Puranic references fit in?

The Puranas themselves of course do not give an absolute date for these events, in the modern sense, since they did not use our calendar.

Scholars study the king-lists in the Puranas, calculate a likely average number of years for each reign, and then give their dates. The Puranas may simply give the main kings, leaving some out. That may explain why scholars calculate more recent dates for the events.

I believe Aryabhata, a brilliant ancient mathematician, calculated the date of Krishna’s appearance, 5000 years ago, based on archeo-astronomical information in the Sanskrit texts. I would go with those dates.