Erwin- could it be that not all Insurance companies/car dealers report to carfax; not to mention people who are involve in solo/minor accidents.
Eg: My 1990 Acura Legend was smashed in the rear while parked in front of my apt. by a minivan who lost control. I was 100% clear; my rear control arm broken, bumper totaled, etc. I had car towed to my acura dealer body shop(hey, I wasn't paying a dime,so I had the culprit pay top dollar) and they fixed at a cost over $3000, plus I got rental thru them on this dude! later sold the car and told the buyer about the fix; he couldn't tell anyway. To this day, it never shows up on any carfax report; the car even changed owner again! So, it looks like carfax is reliable but up to a point!!!