In the late teens, through The Great War, Ithaca Gun Co. phased out the use of composite iron and steel barrels, making a number of their entry-level grades that differed only by barrel material redundant. They dropped the No. 1 Special and combined the No. 1 and the No. 1 1/2 as the New No. 1 in late 1919.
No. 1 Dec. 1919 Catalogue.jpg
By the way, a 1927 vintage NID .410-bore would have started life chambered for the 2 1/2 inch .410-bore shell. The 3-inch .410-bore shell was introduced along with the Winchester Model 42 in 1933.