> But in all 4 cases, it clearly and significantly shows that people with low actual ability overrate themselves and people with high actual ability underrate themselves.

I read the data quite differently. I read that people don't use the full scale when rating themselves. The self rating scale goes from 60 to 90. If you correct for that, people kind of seem to do a nice job in self evaluation.

It can be explained, too. People have social pressure not to rate themselves near 100%, nor in the bottom half of the scale.