I've been unable to resolve this and about to pull out my remaining hair. There are other similar posts such as this one which I wanted this to be a response to but I am unable to post there due to being new and yet without any earned reputation.
I've troubleshot it down to expose an error related to the month but that is as far as I have been able to get to at this point. The attached screenshot show the erroneous results
I don't want to manually retype the dates for all my data. Does anyone have any ideas how to fix this?
Some related information
- Excel 2013
- data was cut and paste from the web using Chrome
- I've used many typical tricks to strip formatting
- I used text to columns at some point
- I've tried many solutions that I've found and none of them make a difference

Column A = day Column B = Month Column C = Year Column D = DATE(C#,B#,A#)
I've created a much clearer screenshot but am not sure how to edit my post or add it to this comment, working on that
– Ack Feb 25 '20 at 22:18=DATE(2020,31,1)it returning the 1st in the 31st month of the 2020 year. So the 31st month is 2 years and 7 months added to1/1/2020you sure you do not want=DATE(C2,A2,B2)where the Month is actually column A and the day is column B. to me the formula is returning the correct value. – Scott Craner Feb 25 '20 at 22:4312, you are getting unexpected Date,, considering01/31/2020returns07/01/2022,reason is that Excel add19to moths, if U use this=DATE(YEAR(C2),MONTH(B2)-19,DAY(A2))inD2, you get12/01/2020, hope this help you ! – Rajesh Sinha Feb 26 '20 at 08:32