I spent a lot of time trying to figure this out and found the easiest way to do it. Below is the detail.
Excel’s serialized dates are the number of days since 1/1/1900. In order to figure out the date again, we have to add the serial number worth of days (subtracting one to account for the inability to not count 1/1/1900 as a day).
|1||Original Date||Serial||Formula||Converted Date|