Not gonna count on cookie chains, since the 3 times I've gotten them, I've only gotten the guaranteed 5 cookies out of them. 10% chance of not getting the next cookie? Yeah, no, unless I'm to believe I've really had a 1/1000 event happen to me.
EDIT: OF course to make me look like a fool I get the highest then-possible amount, getting to the 666,666,666,666 cookie. Oh well, not like it was a BAD thing to have happen, and now I'm gonna get one of those +15%s sitting there once I have enough again...
EDIT2: First full cookie chain. Kitten Engineers, you're nearly mine!