The year number of the Hebrew Calendar represents the deemed number of years since the Creation of Man, calculated by adding-up the ages of those notable individuals in the Bible back to the Creation of Man.
In 1582 AD it was Decreed by Pope Gregory XIII that the Julian Calendar was to be reformed and that - at the instituting of the corrected form of the Calendar - ten days were to be omitted from the extant Calendar; it was hence Proclaimed that the day following Thursday 04 October 1582 would thenceforth be designated as Friday 15 October 1582.
With respect to the designation and inclusion of Gregorian Year Dates preceding the advent of the modern Calendar [1582], it should be noted that these are rudimentary and are included here for exemplification purposes only.