How accurate is Carfax reports?

The problem with Carfax is what’s NOT on the report. None of the oil changes on any of my vehicles will show up on a carfax report because I do my own oil changes and most other maintenance. Carfax gets a lot of their accident reports from insurance companies, but in many states that information is not allowed to give to third party. If there is something on the report then it’s probably true. But you never know what’s NOT on the report.