Is there an optimal way to store dates? i.e. strings, chronotypes (one type or mixed?)?

I have some dates of varying precision, e.g. some just years while others are specific dates, and I was wondering whether it makes any sense to mix these in the value part of the EaV triple?

Or split into separate triples for each chronounit, e.g. :document/year, :document/month, :document/date, etc