This is not proof positive, but here is a little more evidence that the single line barrel address might have been the early .410 barrels with the two line address coming later.

See this link: www.gunbroker.com/item/953199243 This is a 1921 Combination Kit in a Style 1 case. Photos 5 & 13 of 16 show the one line barrel address on the .410 barrel.

Also see this link: www.gunbroker.com/item/955514841 This is a 1922 Combination Kit in a Style 2 case. Photos 1 & 2 clearly show the two line barrel address on the .410 barrel.