One thing to keep in mind is the modern demographic finding that the Confederate losses during the Civil War were grossly underreported in the past. At a certain point Lee was aware that his telegraphic communications with Richmond were routinely intercepted. They were literally being printed in the New York Times. It became Lee's policy to communicate with Richmond via courier. The numbers available to the public were deliberately low. As a result, the actual casualty returns from his army were significantly higher than what is published pre 1990 publications. The traditional loss during the Civil War was pegged at 620,000. Using modern demographic tools, an additional 130,000 have been added to reach a total of 750,000. The vast majority of these additional casualties were Confederates.
Historians will tell you that Union record keeping was more accurate than Confederate. There are a lot of very easy to understand reasons for that. Simple loss of records is one factor. Commanders, not just Lee, on the Confederate side, e.g. Hood, habitually underreported their losses.
This is not meant as a critique of the casualty reporting on the Southern side at this battle, rather a statement of a general skepticism of Confederate casualty reporting.