inter gravissimas

Due to the calendar reform of 1582, most of Italy, Spain, Portugal, Poland and Lithuania did not have these past few days in that year—the date jumping from the fourth to the fifteenth of October.
Pope Gregory XIII issued his papal bull, Inter gravissimas, in order to correct for the drift in the Julian calendar but certainly did not considered it a name sake or legacy item, and it was only later historians that sought to reconcile earlier dates on civil calendars, prolepsis, applying the new conventions backwards (which also marked the beginning of the new year with different dates, city by city), that came up with the designation. Confusingly, France implemented this change around two months later, leaping from the ninth to the twentieth of December. Great Britain, Tuscany and the Protestant Kingdoms of the Holy Roman Empire waited until the 1700s to make the change. I think all these people had the good sense to stay in bed and wait for tomorrow.