This only upsets really anything in the BC era. We got the Julian calender [which is similar to the Gregorian caldern we used today] in 46 BC. From then on it was pretty easy to keep track of history [somewhat].

Before that, historians had to estimate a bit more and were probably off by a couple of decades. HOWEVER, civilizations like the Maya who developed their own calender that we can interpret allow us to be more accurate in history.

Also, we have geologic dating [that thing with rocks and half life of isotopes] to get certain civilization births and downfalls to the right century.

In addition, we had many BC civilizations going on at the same time, we can use many of their historical writings and timeline to pair it up with others.

So, yes there is some inaccuracy on when some historical events occurred BC. While some can be debatble whether they happened during that date, a lot actually aren't and are pretty pinpoint accurate [not to the day or month, but maybe the year or decade it happened]