I’m not sure what it is about Cold Harbor but there is evidence that the Union casualty rate has been badly inflated. The usual estimate is about 12,000 killed, wounded, and missing but Gordon Rhea, who is on his fifth book detailing the Overland Campaign, has come up with a much lower casualty list that is about a third of that.
Correct, the casualty figures are all over the place.
Rhea’s estimates are very much lower than other historians of the subject. The 12-13 thousand figures are for the three days fighting at Cold Harbor. The 7,000 figure is for the casualties of three infantry Corps attack on the 3rd of June. That is about 19% casualties among the attack forces.
At Gettysburg, Pickett’s casualties in the attack on Cemetery Ridge was about 7000 men. This is about 55% of the Pickett’s force. Grant is called a butcher for the assault at Cold Harbor, while Lee gets a pass on the slaughter at Cemetery Ridge.