Sorting dates in column

Hi, not all my photos have Date Taken but most do. I checked the exif data and confirm these photos don't have Date Taken. That means under Date Taken column, there will be blank cells where there is no data.
I tried to sort the Date Taken column by clicking the header as well as using right click>Sort by>Column>Date Taken. Unfortunately while these methods do sort to some extent but not all. I also tried to mark the check boxes as well but same result. The reason I wanted to sort is so that I can uncheck the tick box so these files will not be renamed.
I have tried to manually locate and uncheck these photos but I have thousands of photos to rename.
Would appreciate if someone could point out what I did wrong.
Thanks

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