Drk Pwnr Quote -- investigating now. The thing that borked November should have been fixed for the December run, and anyway, it shouldn't have affected the battle-count.
Update: whatever it is, it appears to have only affected singles formats, but it does appear that it affected _all_ singles formats.
Update 2: so the good news is that, like the bug that's causing me to rerun November, the usage counts themselves are unaffected. Which means that the only thing that will affect the tiers is the math that combines suspect and non-suspect ladder stats, which means that the only tier that could possibly be affected will be PU, since NU is the only tier that had suspect tests in December.
Update 3: to be clear, I know there were other suspect tests in November, but those all seem to have the correct battle counts (meaning either PS changed some log format in December (unlikely) or my fix for the November bug broke something (extremely likely)