Accuracy is not a word I would have applied to the Coppock indicator. Coppock did not see it in such terms either. Rather, he saw it as reliable in that it consistently did what it was designed to do, which was "indicate a condition of low RISK for new long-term stock commitment" (Realistic Stock Market Speculation page 26). He specifically said in the words leading into the above quotation that "the technique is NOT a precise timing method". He never claimed precision or accuracy and said that it could be some months either side of the bottom of the market. My own work confirms this. So, I must disagree with your conclusion as to its accuracy. I would be interested, though to see the basis for your claim and to which indicators you compared it and found less accurate.
There is no comparable indicator of which I am aware for the tops of markets. Like all momentum oscillators, the Coppock indicator gives many premature signals. Coppock knew this and warned us not to use it for bull market endings. I have a combination of things that I teach in my seminars on how to identify the condition of the market at bull market endings.