Nibby and nibnose aren’t in the Scrabble dictionary so I try to forget about them lest I get challenged 
I know and used the words nibby and nosey.
Nosey - like having your nose in everyone’s business
Nibby - having littly crunchy bits in it. ex. the cookie had all little nibby bits of toffee in it
So no, not interchangeable at all.
I have never heard nibnose.
I thought nebby and nebnose were Pittsburghese. That said, I do know all three.
I live in northern WV, not too far from Pittsburgh, but I’ve only ever heard “nosey” before.
Another Pittsburgher here. I didn’t know how to vote since around these parts, it’s “nebby” and “nebnose”, with the /e/. I voted technically and said I’d only heard of nosey, but if you said I was being “nibby”, I’d translate it as “nebby” and know what you meant.
Yep, grew up in SW Pennsylvania (Go Stillers!) Although I thought it was “nebby” and “nebnose”. I also know about gumbands, redin’ off the table and dupas.
I have heard (and sometimes say) “red’ up the table”, but I hadn’t ever heard of “dupa” until just now when you mentioned it. So I looked on the web and found this article:http://www.pittsburghlive.com/x/pittsburghtrib/opinion/columnists/heyl/s_603283.html, which seems to suggest that it’s a term of Polish origin. That’s probably why I hadn’t heard of it; in Italian Pittsburghese, we say “cool’” (cf. Std. It. “culo”).
Speaking of etymology, I had always heard that “nebby” was of Scotch-Irish origin, which would be going back a long time, since the Scotch-Irish were among the initial settlers of Pittsburgh after the French and English.
The poll results are giving me the finger.
Native Hoosier here. Familiar with all three.
Never heard of Nibby or Nibnose. I’m in NJ currently, but have lived all over.