Good points, thanks again.
(1) The ReadMe does talk to the size of the TimeChangeRule, and that could be elaborated on. Being very conscious of resources, mostly size in this case, I'm not terribly inclined to check the address. I also see that the Arduino EEPROM library doesn't validate addresses.
(2) Yes that bothered me just a little. Like I said, I didn't want to waste space, but on the other hand I didn't sweat processing overhead terribly, my assumption there being that there just isn't a lot of reason to do time zone conversions very frequently. I'd think once per second would be about it, that being the typical RTC resolution. BUT still a good point that is worth experimenting with. One of those things that I just didn't think through any further at the time.