I would expect your final question is quite dependent on 'where.' Middle class Roman citizen? Likely. Anishinaabe transhumant hunter? Unlikely.

The precision of dates is heavily limited to the precision of their first recording. A Spanish navigator five hundred years ago is accessing a standardized calendar (the Julian, IIRC) and synchronizing that calendar with other calendars every so often. That synchronization continues, unbroken, into our own calendar, so, less extenuating circumstances (like a loss of synchronization noted in the primary source or a disparity between primary sources) we can assume these dates are exact. On the extreme opposite end you have radiochemical dating which can have a minimum error of millennia.

The problem is that histories (where we get a huge balance of our information) are sources written after the fact. In some cases they were collected from interviews, recollection, from traditional narratives, all of which have some degree of inaccuracy, and that is if they're recent enough to synchronize well with a dating system.

To my knowledge not every dating system has a "year 1," or [epoch.](http://en.wikipedia.org/wiki/Epoch_(reference_date)) The Hebrew calendar's epoch, for example, was established significantly after the Hebrew people began observing certain lunisolar periods and events. As time has gone on it seems as though most calendar systems have adopted epochs for primarily historical reasons.

This thread is absolutely terrific and has extensive discussion toward this very issue.