I think that the difference in the usage of terms for gun shot wound depended upon the level of expertise at which the notation was made in the records. The Latin terms seemed to be used by the medical professional while "GSW" was made more on the muster rolls by non medical people like 1st Sargeants and orderlies. After all who would be familuar with the latin terms for disease and medical conditons? Even then the Latin term for Gun shot wound was abreviated to "VS".
I was amazed in transcribing one particular companies muster rolls that I was researching, that at the Battle of Shiloh a large number of their muster rolls were very detailed (in my opinion) regarding the wounds that many of the men had recieved during that battle. About 1/3 of the men of the company records showed they were wounded in the "left side of the body". This struck me as unusual for so many men to have the same wounds (about 10 to 12 men) until I realized that they must had to have been in the process of aiming, which exposed their left sides to their enemy, when they recieved a volley fire. It was an interesting snapshot of one instance of their Battle.