Who am I to judge what you find humorous? Laugh away. The day I built the bike, we had just ran out of 650b tubes and there was a trail calling my name, so I used what I had. They haven't flatted yet, so I haven't changed them out. I do giggle a bit at the 29er guys trying to shave grams, but the point was to illustrate that while not the optimum solution, it can and does work. I wouldn't do it to a customers bike, but on that particular day, it offered me some much needed "instant gratification".

Given the choice of waiting a couple of days for the labeled correct tube, or getting in some miles on a new bike, I'm lead to assume you'd stick to your pedantic ways. Perhaps your shop never runs out of any stock. /shrug