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We have to live with the fact that partial dates (year, or day/month, or month/year) are simply not dates.
you can evaluate them as consistent strings (text) that will sort correctly :
right ( "0000" & year ; 4) & right ( 0 & month ; 2) & right ( 0 & day ; 2 )
1 of 1 people found this helpful
Your only other option that I can think of would be to assign values of 1 for any missing month or day so that you have valid dates in each case. Whether that is useful or just misleading depends one what you need to do with this data.
Thank you both for your suggestions, @1-more-thing and @philmodjunk. That's very helpful and sufficient for my purpose!