Just a quick note that I'm taking a look at this. It seems to me that accessing the mbox data is mildly annoying, and that the same data is available by the public archives (in HTML form), so for my own development convenience, I'm going to rewrite this code to be based on the public HTML archives of debian-devel-changes.
I hope to have a more detailed update in a few days. Informally, you can find some code here -- https://github.com/paulproteus/debian-devel-changes-history-extractor . Cheers!
