I had an NID 16ga Grade 3 at one time with a factory Non Selective Single trigger and ejectors.
I completely rebuilt/restored the gun as it was a box of parts when I bought it. So I know the trigger and how it works.
The gun also had an extra set of bbls fitted to it, but not from the factory.
#460060 was the ser# if my mind is still working right.

I also had an Ithaca/Lefever A grade 12ga with a factory Single Non-selective trigger.
I rebuilt & upgraded that gun, so I know that trigger to be the same as the above in design, mechanism and function.

I currently own an Ithaca/Lefever A Grade Skeet Special 20ga w/ factory Non-Selective Trigger & ejectors.
I've done nothing to that shotgun to this point but shoot it. I have taken it all apart for an inspection and cleaning. A factory SNS trigger the same as the above 2.

All the same SNS trigger on the NID and the 2 Lefevers A Grades.
FWIW