That's just it. I don't remember Tony ever saying that. He had that meet up with Paulie to tell him he was bringing Furio over. And then Tony said something like "It's me, then you and Sil together. Pussy answers to you guys. Furio too." Maybe people read more into that than they should and just assume Paulie was the underboss.
Despite what various fan sites or wiki sites say, I don't think Paulie is ever identified as the underboss in the show itself. But he is often identified, either directly or indirectly, as a captain in various episodes through several seasons. Also, Silvio was identified as consigliere once or twice.
Good memory. Unfortunately I forgot the S2 Furio, who spent more time shooting junkies in the kneecap then discussing floor tiles with Carm. I remember that now, you could tell they were all nervous about Furio's appearance. Pussy whined about being upstaged with his FBI agent. And you could tell Paulie was thrilled when he rises above him.
Fansites...yes. When 10 or so start spouting the same information, I believe there's some truth to it. I still do, I've had the same opinions since the show. Remember that Nikki Leotardo rumor? Because of various forums, everyone believed the Members Only guy in Made In America was credited as Nikki Leotardo. And that Bobby mentioned that when you die your vision cuts to black. Unfortunately, this is again because they didn't give us much information to work with in 6B. 6B was a sad case where the sum is less than the parts. Tony gets shot, Paulie watches threes company, Patsy gets time to shine, Benny boils Artie's hand, Chris goes crazy insane. But it was hectic as hell. Which again makes forming conspiracies and far-fetched theories (which I enjoy) a lot more painful.
