Bringing this thread back from the dead, I have switched to yet another system, copied all of the *.rrd files, and while the graphs appear with the old data, none of the new data is appearing in the graphs, including in the system graphs. The system time is correct, so I'm not sure what's going on.
Edit: it would appear the period in which my system was offline, the logging was messed up. Running updaterrd.sh manually produces:
ERROR: illegal attempt to update using time 1251689375 when last update time is 1251697276 (minimum one second step).
I believe I'm correct in assuming that just waiting a bit over two hours will cause the problem to solve itself?