(This Xth century business always bothered and genuinely confused me to no end and everyone always dismissed my objections that it's a confusing thing to say. I'm a bit surprised, but also relieved, to see this thread exists. Yes, please, kill all off-by-one century business in favor of 1700s and 17th settecento or anything else you fancy, so long as it's 17-prefixed/-suffixed and not some off-by-anything-other-than-zero number)