I found Adjuntant General Roger Jones' 1849 report of Mexican War casualties at:
http://history.amedd.army.mil/booksdocs/mexicanwar/casualtystats/MexWarStats.html. He acknowledged that the oft-cited figures (see e.g., Heitman and Bauer) from the 1848 report were in error. General Jones states "The aggregates reported in the several recapitulations of 'loss in battle,' do not agree with those reported in the first tables of this series. The losses in battle are obtained from the field reports of the commanders, forwarded immediately after the action, and are liable to revision when subsequently reported in the regimental returns and company rolls."
This is another example of modern historians repeatedly relying on a flawed prior work. Score one for Justin Smith.
The adjutant general also indicated that his 1849 statistics were not perfect: "The statistics of the war are presented as close approximations only; the difficulties attending their compilation being so numerous as to render the attainment of positively accurate results impracticable."
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