I wrote an explanation of the Coppock indicator in Shares magazine December 1999. It only gives one signal - to begin long term accumulation when it turns up from below zero.
The article you quote uses a different method to calculate the indicator. I use Ed Coppock's original method. It does not give many signals, but that was the whole point and as Ed Coppock intended.
It is not a matter of belief, but fact, that the original method gave a signal in 1988 on the DJIA and has not given another since. This is not surprising considering the DJIA has been in a bull market since 1988.
Whether the method used by the writers of the article is better or not will be proven over time. However, for the present, my instinct says that the DJIA has not fallen anywhere near enough to signal the end of a bear market (April 2001).