This is a good over-view of Army Ground Forces / AAF usage, continuing just post-war. Field Artillery pilots were both officers and NCOs finishing their specialised training at the Air Training Dept. at Fort Sill OK. L-4s went to AGF, L-5s mostly to AAF units.
https://history.army.mil/html/books/...ub_70-31-1.pdf
Infantry Divs. were assigned 10 pilots, Armoured Divs. 8; Corps Artillery Groups and Air Sections 2 pilots. Organisations above Corps 1--5 pilots, could be 6 depending on situation. 12th. Army Group (1st, 3rd, 9th 15th Armies) used 2-number codes plus letter, 5th, 7th Armies had 1 or 2 letter codes with no aircraft letter attached.
(Fort Sill as a base dated back to 1915 when artillery-spotting training was combined with Field Artillery).
Nick oops just missed post above..