But, that's not how it works; AppleCare and AppleCare + are dated from the date of purchase of the Mac/product. You'll never get 3 years and 59 days of coverage, you'll only ever get 3 years.
This is confusing though, I'll give you that. I worked at Apple as a genius for a number of years, we had a new store manager who, when he first started, thought the warranty tacked onto whatever time had elapsed, too.