You're right, they also pull from the DMV records. If an accident is so
slight as to fly under the reportable threshold established by the DMV,
there will be on data for Carmax to pull. Carmax also pulls from smog check
records and from reported dealer service, but this only gives mileage data,
not wreck histories, so I ignored the data source.

Your original post implied that your only interest was in the wreck history.
Wrecks are reported through the insurance carrier. My state, and I have no
reason to think other states would be different, requires ANY damage that
exceeds $750 to be reported. If one is driving along minding his own
business and a fence post jumps in front of the car, and the damage is
greater than $750 (I might be wrong, in which case the damage is greater
than $500), then one must file a report with the DMV. If another car
suddenly appears in your path, odds are very good that the damage will
exceed $750, and thereby trigger a report to the DMV.

If the damage is under $750, then it would likely be very minor anyway, and
I'm not sure why you would care if it was listed at Carmax or not.

You are the one that made the charge that a wreck did not show on Carmax
records, I'm only trying to help you understand the conditions where that
might be true.

Let me give another scenario. The car is older, say 10 or more years, and is
in an accident that is not all that traumatic but the repairs exceed 70% of
the value of the car. Given labor rates and parts costs, 70% of a low-value
car is pretty easy to do in a very minor accident. IF the owner even called
the insurance company to see if the repairs are covered, this will trigger a
salvage title because the insurance will determine the car to be a total
loss. Since the repairs would exceed the $750 limit, there ought to have
been a report filed with the DMV, but since the owner opted to do the
repairs himself, he might have skipped that part. If the car was not covered
anyway, then the owner might simply undertake the repairs and never call the
insurance company, and Carmax would never know since the state was also not
notified.

You discovered that Carmax is not perfect, all I'm doing is telling you what
might cause the loop hole that you found. You can bitch at me if you want,
but all I'm trying to do is help you understand the pitfalls that you
already discovered.