Those anonymous entries are not necessarily bad events, usually they are just registrations and such.

One thing to keep in mind with carfax (and the other similar services) is that they are FAR from comprehensive. In other words, if carfax says something bad happened to the car, they are probably correct. If carfax says the car has a clean history, they could easily be wrong because their database may just be missing the data on the bad events that happened to the car.