[vidarh]

A more realistic case for you: People make far more mistakes than you think. Having done genealogy recently, the number of documents with people messing up their own birthdate or name is staggering. On top of the much larger number of registers where someone else have taken the information down wrong.

[evanb]

Or when there's a difference in convention. For example, the European convention dd/mm/yy[yy] and the US convention mm/dd/yy[yy].