Edwin Coppock said the indicator only gave one signal. That was when it was below the zero line and turned up.
His only reference to it crossing the zero line was that by then we should have completed buying.
In my observation, the best signals come deep in negative territory. Indeed I cast doubt at the time on the last but one signal on the US market which was very shallow. Sure enough, the Coppock soon turned down again.
We have now had two signals on the US market in this bear market that look to be premature. This is not entirely unprecedented. If you think about what the Coppock Indicator is - a long term momentum oscillator, it can give premature false signals in a long trend. If the bear market had been short, the first or second signals might have been OK. However, this is now one of the longest of bear markets in the US and we should be cautious of premature signals.
The best defence is Coppock's instruction to start buying strong stocks when you see a signal. If their trends fail, you get out of them, as always. If there are no strong stocks, then you wait until they appear. A strong stock is one making new highs - i.e. trending up.