Has there ever been any documented circumstance where significant inside information became public and known thanks to a trade? Most often, the trade is made at the last minute, and the information gets subsequently revealed anyway. And it's impossible to tell whether somebody is an inside trader, a wealthy gambling addict making a stupid decision, or hypothetically a foreign agent pretending to be an inside trader to make people believe in a particular outcome.

It's impossible to know anything for certain; almost everything is probabilistic.

Also I'm not sure how to interpret your criteria because timing matters, I don't think saying 'it gets revealed in the end' is very meaningful.

Anyway, on Polymarket specifically, sure, military strikes are a common one. Seems like a useful signal to go hide in the basement. Outside Polymarket, there were insider trades in 2008 that I'm sure were useful.