Saying Saturday's military strikes triggered the Polymarket's 'No outcome' resolution for June 19th and 20th feels a bit like putting the cart before the horse, doesn't it?
Those earlier days resolving with 'No' simply means nothing happened then, a fact in itself.
What actually happened on the 21st doesn't change the absence of action two days prior, it's just a separate event.
For example, if I put a pound on the horses not running on Tuesday because of rain, and then they ran on Thursday, my Tuesday bet still resolves 'No race' not because of Thursday's race, but because of Tuesday's rain.