perhaps along the lines of :
parse the scanned/ ocr'd DLN to var $_licence_number
enter find mode
set field (TBL::drivers_license_number) = $_licence_number
IF get found count = 0
# new data, do null
# the record has been found and is hence dispalyed
i.e. use Perform Find under the Found Sets Category, not Perform Find/Replace under the Editing Category
Set a global with the scanned number. Create a relationship to the table with all the data in it (global to dl#). If Valid (field in full table) should return a 1 or 0 that you can test on.
If you are doing this using version 12, it might be worth seeing if running a simple query with ExecuteSql serves your purposes well for a quick check to see whether or not the record exists.