I remember learning that some Asian Nations don't use the Gregorian Calendar, but do in certain things, which kinda confused me and kinda didn't but yeah.
What really gets me is, did the greeks really label they're things as 574 B.C or whatever, did they use years? That confuses me so much, and causes me to explode. Also, closer to time of A.D. did we (Europe) use A.D. immediatley after Anno Domini's establishment. I'm really in the state of Double You-Tee-Eff right now.