OH, and if Watchtower needs to do so, they will come out with new light that a Bible year is 365 days or even adding in the Leap Year days if need be. Or they can add in the 13th month stuff.
They already made the 1975 stuff up when they needed to build a whole new empire with new printing presses. They made up the overlapping generation stuff. They will make up some new crazy nonsense in the distant (or not so distant) future when they need to. They will just vote on it, and God will contact 2/3rds of the Governing Body.