Your bike computer, especially the way you calibrated it, is probably more accurate than they way the people running the century measured it. For example if they used a car to measure it makes sense that it came out shorter as many car companies have their speedometers very slightly inflated. One of the reasons for doing this is it eliminates a few miles the manufacturer is responsible for on warrantees. For example when your car shows 36,000 miles it really has only about 34-35,000 miles. they save millions of dollars. Recently when my car hit 36,800 miles I had some transmission problems that eventually came out to around $1500. My dealer wouldn't cover it saying it was way past the 36,000 miles. I threatened to have it verified and said I would sue them. They seemed to know what I was referring to and said would get back to me. The next day said it would be covered under warrantee. Check your car against your bike or one of those speed checkers you will find your speedometer is off by a few percent. Oh BTW you didn't do a century. Go back and re-do it with the extra 6 miles.