So I sold one of my ar 15 style “other firearm” today that was built from a stripped lower and registered as such. The FFL that the buyer chose was giving me a hard time because the lower didn’t have “other” engraved on it. I explained my research told me as long as it was built from a stripped lower and registered as such it shouldn’t matter if “other” is engraved on it or not. It was never a “rifle” or a “pistol”. He said he will do his own research . I agreed.

Does anyone here know for a fact that I’m wrong about this?

A stripped lower that was never registered as anything other than that, is always an “other firearm”. Correct?

You are correct. However, from the FFL standpoint.. they would have to agree that your build is substantially identical to what the NJSP opinioned was legally considered an other. If you used a different brace, or vfg than they can simply say no due to many unknowns. 

It doesn't matter what's engraved on it. 

"Make" is the importer (if there is one) and manufacturer that is on the serialized part.

"Model" is not required.

"Type" is based on it's current configuration. Who cares, or can prove, what it was prior.

"Caliber" is based on the barrel's chambering. What it says on the receiver is irrelevant.

Thank you gentlemen ....

seems like the FFL called “a buddy” and the buddy cleared some misconceptions he had. The sale is going through apparently .