Interesting comments. I really enjoyed the history lesson as well as the different standards based on club or individual preference. It seems clear that when riders on this or similar forums talk about a century ride they use whatever "standard" they prefer. Personally, I'm partial to the sixteen hour standard for centuries or any other ride...Henceforth whatever distance I cover in a continuous sixteen hour time frame will be considered as my ride distance for that day.
I now have a standard, which was my intention when posting this thread.