Here's one more clue which the folks at the National Archives could use.

In the Miscellaneous file, there is one card for:

Bridges - Rob’t T.
Lt.

which notes

Reference Card.

See Manuscript No. 889, page _____ [blank]
Under Sentence
G. C. M. O. 198 War Dept.
Dated - Aug/ 1864

General Index Card
This card must not be taken from the files.
6413

M347: Unfiled Papers and Slips Belonging in Confederate Compiled Service Records