No. However, what I am certain about is that he did not use an average for the month. In Realistic Stock Speculation page 25, Coppock says, "On the same day of every month, note the closing price of the DJI." So, you can calculate the indicator for any date you like in the month. The most conventional date to use though is the last day of each month. However, it is quite clear he did not use an average price.
The Coppock Indicator was popularised in the UK by Harold Wincott and Hugh McDougall. They changed the method to use the average value for the month and also only use a 12-month rate of change, rather than Coppock's original method. (Source: How Charts Can Make You Money by T.H. Stewart, page 87). This seems to be the method used in the Investors Chronicle. I have not made any attempt to compare the two methods.