Mostly oout of laziness, I've put off upgrading to 2005.45-8. So I just took a look at the download areas on mameo.org and at http://europe.nokia.com/nokia/0,,79636,00.html and found this:

Nokia_770_SE2005_3_2005_51_13.bin 27-Jan-06 | 59.1 MB | English

(file is listed as Nokia_770_3.2005.51-13.bin on the other system, size and md5 hashes are identical)

There's also a PDF.

NO idea what is in this and I don't see anything in the maemo user, developer or announce archives.