Year zero
Historians have never included a year zero. This means that between, for example, and , there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usage "anno Domini" 1 is preceded by the year 1 BC, without an intervening year zero. Neither the choice of calendar system (whether Julian or Gregorian) nor the era ("Anno Domini" or Common Era) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood.
Year 10,000 problem
The Long Now Foundation is attempting to foster the custom of writing years with five digits, so that the year 2022 would be written as "02022". This would preempt the Year 10,000 problem, but would in turn be susceptible to the "Year 100,000 problem".