Is a copy of the Chaplain Plummer court-martial transcript available,
or is a trip to the National Archives necessary?

Accounts in secondary sources are helpful/essential reading--but I think--I know-- the search must begin with the official records. And be warned, these records can be a swamp--they can reveal as well as conceal.
I'm struggling with the over l,000 pages of the Flipper trial record and related documents, and it will be a cold day in hell before I develop the courage to dive into the l7 (yep, that many) rolls of National Archive film that make up the record of the Court of Inquiry and later court-martial of Cadet Johnson Chestnut Whittaker.

But the daunting heft of these records did not stop the Army Board for the Corrections of Military Records from granting Lt. Flipper an honorable discharge in l977, and President Clinton from granting the unfortunate Lt a posthumous pardon(the first ever) in l999. Also, sometime in the early 90s (I am not sure of exact date) the army issued Whittaker a posthumous commission.

Correcting the record can be a good/proper and necessary thing. As long as corrections are based on a thorough examination/understanding/analysis of the available record.

I would urge supporters of Chaplain Plummer to do their homework and never allow sentiment to trump evidence.