Fair point, and you're right. Doenitz ordered that all boats departing in August were to use the North Sea route, and yet two boats did venture into the Channel in October 1939, and both were lost. I'm not sure if any boats braved the channel between then and 1944, but it would seem that no less than eleven boats tried their hand against the invasion. There may have been more, but that's how many were lost between June and August 1944. Several more tried in 1945, with similar results.
http://www.uboat.net/maps/channel.htm
My point was the standing order against using the Channel for transitioning to the North Atlantic from Germany.