Coinmarketcap have it right ? Click what ever coin you want and see the chart at the bottom page, Its complete from first day the coin born
What I saw, and this is not using JSON (just on html page), it only gives the open, closing, high and low prices for the day.
I wonder if it would be sufficient just to use an average of these four numbers for each day, for the price. Or if it should be down to the minute.