What I mean by that is when did people start saying "he was born on October 13th". This has been bugging me for a while now, additionally, how did people keep track of dates back in the day? Thanks for your help :)
There are some previous answers in the FAQ that may help:
How confident are we that the year is actually and exactly 2016? Is it possible that at some point in the last 2000 years there were any significant timekeeping mistakes? and Did people in the Middle Ages call the year "one thousand and one" or "ten oh one"? by sunagainstgold
At what point did society begin referring to the year in modern terms (2012 etc)? by /u/Algernon_Asimov
Was the millennium from 999-1000 ad marked in any special way? by /u/savvysioux
Did people in 999 AD celebrate the new millennium? Were there any doomsday predictions similar to Y2K? by /u/haimoofauxerre
And if I may add, an answer from me: