How has it come to be known today as the year 2015? As christ's birth being year 1. What culture has been recording all these days so meticulously that we confirm the date today to reflect the actual time between present day and year 0? For example the Chinese new year is different than other countries. what other cultures calendar got scrapped to make way for the general consensus of the year we use in our present day to day.
In Japan it is currently Heisei 27. The twenty seventh year of the reign of emperor Akihito. This year is used on all official documents, birth years, drivers licenses, etc. Although Japanese people are aware that for much of the world it is 2015. And you do see this year used in Japan as well.