Where did you find the record for Lewis in the 16th Mississippi and his discharge for medical reasons in 1862, and in what capacity did he serve? I could not locate.

I am aware however, that many blacks served as cooks and alongside their officers masters. And some did serve in rifleman rolls.

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“Blacks did not serve in the Confederate Army as combat troops. Blacks were not merely not recruited; service was actively forbidden by the Confederacy for the majority of its existence. Enslaved blacks were sometimes used for camp labor, however.”

https://www.bing.com/search?q=blacks+in+the+confederate+army&FORM=QSRE1