This means, in general, that if the real-world UTC date is 2016-09-22 (as it is for the initial version of this post) then the in-game date is 3302-09-22.
At first, this seems all well and good from a logical standpoint. Just add enough full years to real-time, and you can make translations between the current date and in-game events fairly simple.
However, I'm worried it might break down when things like leap years come into play. (Assuming the game runs long enough.)
As we're most accustomed to experiencing them, leap years are fairly easy to follow - just expect a 29th day in February every four years. If it were this simple, then there would be practically no problem with syncing a game's future setting with our current calendar. You'd just pick a year that's at the same point in that four-year cycle as the real world is, and be done.
Unfortunately, it's not quite that simple. The Gregorian calendar skips leap years every hundred years, unless the year is divisible by 400. See the below psuedocode from Wikipedia, for another way of understanding this schedule:
if (year is not divisible by 4) then (it is a common year)
else if (year is not divisible by 100) then (it is a leap year)
else if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)
If that hurts your brain like it does mine, maybe CGP Grey can help.
In any case, this would appear to set us up for years that will end up being leap years in the real world which shouldn't be leap years in-game (or vice versa) unless the time offset of the game universe was specifically planned to account for this. Sure, this could take a few centuries. But it still seems fairly possible.
So, I guess my question can be summed up as this:
Will the in-game calendar ever fall out of sync with the real-world calendar due to leap year differences? If so, when?
P.S.: We're not even gonna get started on leap seconds - for the purpose of this question, let's just pretend they don't exist.