Well if you have the first 20 characters and you have access to a Disk Editor, you may be able to search your disk for the first 20 characters and see if you can find the rest of the serial number. I don't know if it works with modern versions of Adobe software, but it used to work eons ago. Of course if you work with a disk editor, you want to make sure you do not edit the contents of your disk by accident. That could be a problem.
