And an explanation for my problem:

The original issue was and is, that I programmatically have to change alle dates to dd-mm-yyyy format. The dates are imported from other systems, and some of these are in the format mm-dd-yyyy. Dates that are already dd-mm-yyyy shall not be converted, so I want to check the format before conversion.

When the sheet is done, the data will exported to another system, who cannot check if the dates are in the right format, but expect them to be dd-mm-yyyy. Therefore I (or rather those who uses the sheet) have to maked sure all dates are formated correctly be the export.

Jan