[Noah930]

Carfax (and the other similar services) seem to just check DMV databases and insurance company databases. If an accident wasn't entered into the database (i.e. because it wasn't reported to insurance, or if the bodyshop or insurance company fixing the damage didn't enter it into their database) then the incident won't show up. These databases also get purged after time if there is no activity. For example, California DMV tosses old info if there's been no activity on a vehicle after 5 years. I'd bet other states have similar archival policies. So Carfax can only look so far back, as their sources for information don't have that stuff available, anymore. Run a Carfax on your 20 year-old Porsche, and you'll note that the records only start in the late-90s, for example.