Do you have mods activated?
One aspect of what you are seeing, is the Save "time" of the game. Another is that the game counts in several different ways, depending upon where you are in the game's structure. With one method, the game starts counting at "zero", and another, it starts counting at "one" (two different programmers working on two different parts of the game's code). Plus, the game does not understand "days" as such, but rather as 1440 minutes, aka: 86,400 seconds, aka: an exorbitantly high number of computer "clock" ticks - or mili-seconds, determined by the cpu "clock" cycle... It also does not understand what a February 29 or April 31, June 31, September 31 or November 31 are... but they are in the "dating" system that was written by the human programmers for the computer to follow... the later in the game, the further off the game's "day" count is... I don't know if I'd call it a "bug", or just poor quality control...
