The share price likely wouldn't reflect insider knowledge. To see this, take an extreme example. The CEO owns less than 1% of most publicly traded companies. Even if he was allowed to sell his whole position without public disclosure, it wouldn't affect the stock price that much. Say he wakes up and finds out through insider knowledge that his company will go bankrupt tomorrow. He sells all his shares today. The stock drops a bit. It doesn't go to 0 just because he knows it should.

A stock price reflects a weighted average of individual investor's knowledge and their capital.

(Efficient market gets around this by assuming people are cool with not just selling the stock but shorting it all the way until it is as low as they think it should be. People don't tend to bet the farm (or have the ability to borrow funds to bet the farm) like that.)