Still more than anything that @GlueStick did in the Air Force.Can't say how they decide who shoots and who spots; but each member of a team goes through Sniper School and is capable of doing either job. That aside, Kyle was also a SEAL, and even outside of special forces, shit changes as needed. Snipers don't always operate as a sniper team, they can go on patrol with a regular platoon/squad/fireteam; then if tasked to provide overwatch, then they can be alone in their perch/hideyhole. Then whoever they bait and shoot only has one witness. It's way too complicated to even theorize how every kill went down; because the first rule about SOPs in a warzone is the plan always fails, and your backup plan fails, and your second backup plan fails.