Reliability Prediction is an excepted engineering process and in my experience with communications equipment predicted reliability has been quite useful evaluating products over my career.
I really don't know how CR performs their analysis but if they use reliability predictions that are based on component failure rates they probably have a reasonably good idea of what the Model 3 reliability will be.
Over time the reliability of the M3 is likely to improve ...my rule of thumb with cars is never buy the first year of a refreshed existing model and never ever buy a first year new model .....
...