As technology improves, the extent of "recoverable" expands. E.g. shale oil was unrecoverable oil during the industrial revolution and through the mid-20th cen

As technology improves, the extent of "recoverable" expands. E.g. shale oil was unrecoverable oil during the industrial revolution and through the mid-20th century. Further, efficiency of utilization increases with technological advancement. I don't know about coal at this point in time, but I can guarantee you the coal-burning plants of today are getting more electricity per ton(?) of coal than a plant in the early 1900s.