Wow!
I would guess you never lost power. It could be connection to the clock only. Did you lose trip mileage counters, too? I am guessing NO cause those do not disappear with power loss.
Do an experiment. Disconnect the battery for a few minutes, and reconnect. If you only lose the clock, but nothing else.. Well, that will only prove that all other data does not disappear with power loss, but nothing else.