According to the general worldwide* concensus the current year is 2018 or to put it another way two thousand one hundred and eighteen years have passed since a particular event** happened but how sure are we that the year count since that event is accurate?

I'm gussing that the Roman Catholic church has a near continuous record along the lines of Pope ABC was annoited in the year X and ruled for Y years and that their records start towards the end of the Roman era which would have had a similar count based on the various Emperor's time in power but are there any gaps in the records where a year or two could've slipped through the cracks, are there any instances where someone came to power who thought it was a different year and therefore imposed their new count on the populace?

I know the was a change in the year count when the Gregorian calendar supplanted the Julian one, I'm more interested in minor slips up in the count here and there

---

*Yes, I know that culturally some places make use of a different year count such as Buddists saying it's year 5,000 or something and Islam saying it's year 1,400ish and Kurzgesagt saying it should be the year 12,018 but for the most part 2018 is the accepted year

**I'm ingoring that the event in question may or may not have actually happened and if it did it may or may not have happened on what would now be considered to be year one