The POIUtil.cfc by Ben Nadel is a great wrapper to the Apache POI project. I am using it in a current project and have come to certain caveats that I needed to extend the library. Ben, hope you are reading, I sent you an email with the update.

Anyways, to sum up the problem

Excel stores dates as numbers therefore the only way to determine if a cell is actually stored as a date is to look at the formatting.

Enter a little digging in the docs and the API and you find the famous HSSFDateUtil class. This class contains a bundle of static methods for you to check and validate date formatting in excel.