Number Format Stuck and Can't Change

It's difficult to say much without a sample file or more information. I would guess that those 5 digit numbers are the corresponding serial numbers for the extracted dates. It should be as simple as applying an appropriate date format to display those numbers as dates. Without a sample, I have no idea why Excel is not allowing you to apply a date number format to these cells.

My older version does not have the AGGREGATE() function, so I get an error. It appears, though, that you are concatenating an empty string "" onto the end of the formulas output which would effectively convert the serial number to a text number. Number formatting has no affect on text strings, so they will not respond to the number formatting.

Why are you adding the empty string? My first thought would be to remove that at the end of the formula, but you may have a reason that I am not seeing for having it there.

I'm not sure how strictly to apply Chesterton's fence (https://en.wikipedia.org/wiki/Cheste...on's_fence ) to spreadsheet programming. If you don't have any idea why the null string is appended to the result, then I might make a copy of the spreadsheet and remove the appended null string and see what happens. If the spreadsheet works, then leave the number to text conversion out.