Creating or using fuzzy or wildcard dates

I want to create a field or use a field that will allow me to create "fuzzy dates".  I'm in a business where I want to create records containing a date field.  But, the date field sometimes needs to be flexible.  Sometimes, I know an exact date, like "1 January 2001" or "01/01/01".  But, sometimes all I know is that the event happened in 2001, or that it happened in January 2001, but I don't know the exact date or the exact date doesn't matter and what is important is that I enter for the record that January 2001 is the relevant event measure.  I have used other applications that let me do this quite handily.  So, for the other application, I can enter "??/??/01" to record that the event happened in 2001 and the month and date is either unknown or not relevant.  Or, "01/??/01" would indicate that I know the event happened in January 2001, but I don't know the exact date in January.  It would be quite rare, if not irrelevant, that I might want to know a month and date of the month, but not the year, or that I would know a date of the month and the year, but not the month (latter seems theoretical, but not practical).  Any ideas?