table::globalDate should be a global field of type date, not text. Then invalid dates such as 2/32/2013 will be caught by FIleMaker automatically and the user will not be allowed to proceed. The loophole in that is if you are using a custom dialog with this field as the input field for getting the user to enter a date. I would not use a custom dialog with a date field for that reason.
Ps. I am thinking in terms of scripted finds similar to these: Scripted Find Examples
Cheers Phil. That points me in the right direction. Good link to the other suggestions for find scripts