but before the announcement they have the choice to postpone their buy/sell decisions based on this internal knowledge - which they obviously do.

I guess that's not obvious to me. The original post here and Matt's article just say they average $100k/day in sales before the buyback and $500k when the stock goes up. Is that $100k unusually low? Like if they average $250k until the week before the announcement, drop to $100k right before the announcement, and then pop up to $500k, yes, it's a reasonable conclusion they slowed their selling knowing the announcement was coming (i.e. had inside knowledge). But I don't see any suggestion that's the case (it may be, I just haven't seen that even suggested). If they average $100k all the time and then sell more when the stock price increases, that's just taking advantage of what the market's offering. I've done the same thing (with significantly smaller numbers :-) ) and certainly had no inside knowledge.

Brian