Microsoft Excel stores date values in OLE Automation date format.
DateTime.ToOADate[
^]
DateTime.FromOADate[
^]
But in your case, 58317 is 1959-08-30. If to add 18263, this is 2009-08-31.
Is one of these dates correct?
In any case, you may merge data from Excel to a database using
Data Merge Wizard[
^] of the SaveToDB add-in.
You may prepare data to merge using Excel formulas. So you may prepare correct dates if you know the converting rule.