While true, the other revolver carbines are basically handguns with a different grip, the frame is the same for carbine and handgun. Take off the stock off, put a regular grip on, and BAM its a normal handgun. If it's built on a handgun frame it'll always be considered a handgun.
Example, Alfa Proj:
The heritage carbine doesn't appear to use a standard handgun frame though. It has a straight grip that's more similar to the winchester 94 than a regular handgun, and I suspect you cannot put the regular handgun grips on it. (if you look it appears to have a metal tang that extends towards the butt stock)
This doesn't guarantee a NR classification, but it's enough to consider it in a different light than the Alfa Proj and Rossi carbines.