I can vouch for Robert on that. I've heard that they have to be reported to the DMV directly in order for the accidents to appear but thats still a mystery. my carfax account expired...
carfax only reports on accidents or damage reported to the DMV as stated above, accidents only get attached to a VIN number if the police were called at the time of the accident (which doesnt happen too often anymore) insurance companies are not required to report accidents to the DMV.