Right, I've seen this kind of checksummung before as an easy way to identify duplicates when batch files are processed. Nowadays one would use message digests (SHA, MD5, etc.) to further decrease the probability of false duplicates. Sometimes, these files are imported into a DB or transcoded somehow. Then, it makes (some) sense to focus on the content only - if one can recover the correct sequence in order to re-compute the checksum. Usually, those DBs contain colums like batchfilename and seqno.
Perlbotics