I feel like an issue with asking for the number of years something long happened to an exact number is exemplified thusly: say something begins January 1, 2000 and ends December 31, 2001. That's two years of length, but looking at just the years you'd think it would be a single year. So there is an ambiguity of a full year in questions like this unless there are generally accepted exact starting dates, which there very well may be.
