One of the most difficult things in technical analysis is to make sure that you are looking at the same time frames when looking at different charts. I am seeing the advance-decline line in a strong uptrend only in the short term. It is difficult to compare such a short term observation to the Coppock, because the latter is a long term indicator and only calculated at the end of each month.
As I have said in my Shares magazine columns, I think we deal with this situation depending on our trading and investment plan. Long term investors ignore it. Medium term investors and traders might sit out the rally waiting for the end of the bear market. Short term traders will trade the rally.