Interesting, but I think there were pre-existing efforts and publications in this area. I was peripherally involved in some systems that related to address matching - and one of the data points included in the barcodes was a "customer id" field that was going to be used for automatic unclaimed mail management - the sender of the mail would receive a list of returned mail from the post-office - and the postage would be destroyed.

There's even some of the original documentation around for parts of it (though not expressly for unclaimed mail) from 98 / 99.

a-guide-to-printing-the-4state-barcode-v31-mar2012.pdf - although the document is dated 2012 - that's just the most recent revision - the original dates back to the June 1998 (as listed on Page 2).

This 1999 document australia-post-addressing-standards-1999.pdf references "Specification Number 203-4-State Barcodes" - which likely would also contains the same information.

Likely to either be:

• Big corporate behind one public IP Address (probably not a problem, and would likely show up in their regular "true up" audits)
• Small pirate with big volume registering unauthorized keys like crazy and either selling them somehow, or installing them onto machines in exchange for money.