The part about introns and exons is very important. Normal ("naturally occurring") DNA has a bunch of extra stuff that is not coded for proteins (introns) and that may not serve much useful function for therapeutic research but are useful as unique identifiers/markers.
The cDNA mentioned in the judgment is not a simple XOR of the original information. It is an XOR of the information after the section of DNA has been isolated, and with all the introns stripped out. Using cDNA, one cannot recreate the original full DNA strand because it is like lossy compression.