It does seem that a lot of the No. 4E and higher were fully optioned target guns. One of my favorite pieces of Ithaca paper --
Ithaca Guns for Trapshooters.jpg
What I have observed from many of the bits of Ithaca paper that Walter has posted over the years is that a lot of these high grade NIDs languished in Ithaca inventory for years. These guns all have 1927-8 serial number by the serial number chronology and here they are being shipped out in October 1942.
Oct. 17-1942.jpg
Likewise, the No. 7E I posted Walter's note about earlier is a 1927 gun by the chronology and being shipped in 1944. Were these salesman's samples or show guns? Did they get refreshed/reconfigured at the factory from time to time? Were they something Ithaca could sell for cash during the war years? Lots of ponderables!