I believe Savage Arms manufactured all the parts except for the compensator on the first 10,000 guns in the first contract. All barrels should be marked with the Savage "S" on the barrel collar, usually on the left side in the 9:00 o'clock position. When production began, it was unclear if any additional contracts would be executed as none of the 10,000 Thompsons were presold and Colt's were still in AOC inventory. Only after additional contracts between Savage and AOC were signed, mainly because of the British orders, were subcontractors used. The first subcontractor was probably Stevens Arms.
Index lines on the barrel collar were not standard on the very early Savage Arms Thompson guns. I have seen many examples of original early Savage Thompsons without the Index line on the barrel collar. As production increased, the line became standard.