I see you entiitled your thread 4-f. Where did you get this calssification from. Was he classified 4-f at some point or was this your play on words or the situation.
On most of the Draft Registration forms there was a place to be filled out for the following: Lost of Arm, leg, hand, foot, eye, or both eyes, or is he otherwise disabled. They kept records; because he would have to be given a classification as to why he was not serving. There would be a record.
He could have become deft from the Army, Navy, and Marines. If he served in a capacity where there was a lot of (1.) heavy Artillery fire. Especially if he served in the Artillery. A lot of the guys who worked near cannons were partially deft or permanently in at least one ear. That would be the one that favored closest to the blasting side of the Cannon or Artillery gun. (2.) The constant barage of Artillery fire. (3.) Being shot in or around the ear. (4.) Bayonet wound to the ear blocking off the ear from hearing. (5.) A gun or guns constantly going off at close ranges of the ear.