Dating the birth, marriage and death of ancestors is difficult. Just finding any evidence for their important dates is a challenge. Politics, religion and science have contributed adjustments to our calendar which make dating past events ambiguous, or at least complex.
Social styles contributed more confusion when dates in the Middle Ages in England were written according to the year of the reign of the current monarch. For example, My 19th great-grandfather, Sir Hugh Venables, Knight and Baron of Kinderton, died "4 Edw. II", meaning that he died in the fourth year of the reign of King Edward the Second.
Medieval English Genealogy has kindly published a guide which translates the Regnal Calendar into our Gregorian Calendar system, (which was adopted in the USA in 1752). Using their chart, I discovered that Sir Hugh died between 8 July 1310 - 7 July 1311 . My genealogy program utterly rejects such a date, but I work those details into the notes, and compromise with 'he died before 8 Jul 1311' for the main entry.
If those were the only challenges in dating ancestral lives, I could cope. There is one more issue, which is random and frequent: the typeset error, or, in modern lingo, the typo. In a book published in 1819, the pedigree chart on page 106 shows my Sir Hugh died "4 Edw. I", meaning 20 Nov 1275 to 19 Nov 1276. Fortunately Sir Hugh signed land deeds after 1276, so I knew to go looking for the correct date of his death, which turned out to be 4 Edw II. The printer had dropped an "I", or maybe the manuscript was sent him that way. Either way, it makes doing the Family Tree a perpetual challenge.
Which leaves me wondering how many dates in my family tree are in error from typos - my own or others, and that I haven't yet noticed. If a family tree researcher isn't born humble, they soon learn to be.