> If I am digitising an old text of unknown origin, and on a page it says "January 12", and on the page after that it says "January 15", can I represent those with a reference to an implicit but unknown year? I don't know the year, but I do know that the January 12 instance comes before the January 15 instance on the next page. And at some future point, we might deduce from circumstantial evidence what year it was and the sequential ordering will still make sense. Relative dates would be useful here.
Of course, if the year is unknown, and could be before ~1918, and your dates are, say, the dates of two letters, you can't even be certain about the ordering of "January 12" and "January 15".