i find carfax to always be pretty accurate. my first E30 listed a possible odo rollback, but i knew about it.
it was reset to zero by a bmw dealer at 7200 original miles because of the infamous E30 jelly odo gears. it even had a sticker on the door jamb stating it.
good thing you have had good luck with your bimmer tho. i just wonder how big the difference is.