This feels more like a misunderstanding of the problem at root. This is not really "the ledger from the parish said May 1860 but the day field was smudged", so

This feels more like a misunderstanding of the problem at root. This is not really "the ledger from the parish said May 1860 but the day field was smudged", so ai can write 1860-05-?. This seems to me to be a problem such as "we have a letter from his wife to him mentioning the great fire of london , so he was alive in 1665 but then his wife re-married in 1669 so he must have died between this two dates, but if we can find his military record then ..." This is a problem of recording the evidence accurately and then the uncertainty comes from inferences from the evidence. I don't think the people who need uncertain dates need a way to write question marks - they need digitised and machine readable evidence. Or did I miss the point?