Do note the gun in question was not an NID, it was a Nitro Special. As to whether or not it is an Upgrade depends upon ones definition of Upgrade. I think of an Upgrade as when ones takes one of the basic models of a particular model & has it "Up-Graded" to a higher grade of that same model gun. Example take an H grade Lefever & upgrade it to an A grade.
With this definition this gun was not an Upgrade as Ithaca never made a Nitro Special in a grade such as this.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra