Papal trivia: Although the last Pope named John was number XXIII (23), there have actually only been 21 Popes named John. John XVI (16) was an antipope later removed from the list and John XIV (14) was listed twice due to a medieval counting error.
There have also been kingly counting errors. Edward I of England was actually the fourth king named Edward (after Edward the Elder, Edward the Martyr, and Edward the Confessor). However, the first three ruled before the Norman Conquest in 1066. Thus, Edward I was the first Edward after the Conquest, so I’ll give them a pass on that. Then, there was no Edward V (5). The boy who would have been Edward V was one of the Princes in the Tower who was (probably) murdered by his uncle Richard III in 1483. When his father, Edward IV (4) died, his son should have succeeded him, but since he was in the process of becoming dead, he was never crowned. Therefore, when Henry VIII’s son Edward succeeded him in 1547, he did so as Edward VI (6), even though he should have been the 5th (or the 8th if you want to count the three pre-Conquest Edwards).