Easter schedule dating system
The usual statement, that "Easter Day is the first Sunday after the full moon that occurs next after the vernal equinox", is not a precise statement of the actual ecclesiastical rules.
Nonetheless, different means of calculations continued in use throughout the Christian world.
Therefore, the civil date of Easter depends upon which tables - Gregorian or pre-Gregorian - are used.
The western (Roman Catholic and Protestant) Christian churches use the Gregorian tables; many eastern (Orthodox) Christian churches use the older tables based on the Julian Calendar.
In some cases this difference may occur in some parts of the world and not in others because two dates separated by the International Date Line are always simultaneously in progress on the Earth. In 1962, the astronomical Full Moon occurred on March 21, UT=7h 55m - about six hours after astronomical equinox.
The ecclesiastical full moon (taken from the tables), however, occurred on March 20, before the fixed ecclesiastical equinox at March 21.