Thanks for the additional detail from MRB's service file with the 4th Confederate Regiment. Every word you posted is correct. However, this comes from his 4th Confederate file, which covers the period 1861-62. My questions concern MRB's alleged record with the 37th Mississippi Regiment (1862-1865), which doesn't appear to exist, and his oath of allegiance to the United States, which shows MRB to be a deserter.
As mentioned previously, I believe MRB could have applied for pension support without mentioning anything beyond 1862. There is nothing wrong with his earlier record, and the board would have been inclined to believe that he was incapacitated by imprisonment at Camp Douglas in Chicago. The experience had that effect on some men, who never returned to service.