This is my understanding. I believe Silvio has been consiglere for awhile. During Season 1, when Junior was officially in charge - Tony would not have had a consiglere. I guess Silvio was officially just a soldier in Season 1, same as Paulie.

But thinking back to Season 1, Tony would sometimes discuss things with Silvio, before the others. In Season 1 Tony was often running things. (While Jackie Aprile was ill and then behind Junior's back after Junior becomes boss.)

Silvio's advisory role would have officially turned into consiglere after Junior becomes a guest of the government and Tony becames the official 'street' boss. I think its never officially confirmed in the show - just assumed that we understand this when Season 2 is underway.

Thinking back to the third episode of Season 2, remember that scene when Richie Aprile is supposed to talk to Tony outside Satrioles.When Richie starts talking about getting his action back, Tony walks off and just says 'Sil.'Silvio sits infront of Richie and tells him that "No more talkin business with the skipper directly anymore, U can talk to him, but not now and never here!!

I think it's very significant that it is Silvio who steps in here, acting like a consiglere might do. This is before Paulie gets upped to Capo in Season 2, Episode 5 and suggests to me that Silvio is more senior to Paulie until that point.

Also, I think it was significant in Season 2 that some of Pussy's resentment is directed at Paulie. Particularly when Paulie gets upped to 'Capo.' In Season 2, fifth episode - Pussy is talking to his FBI handler Skip about the way he is now being treated. He says "Silvio, I understand, but Paulie." Skip dismisses it with his comment that Paulie is probably just "dizzy from too much hairspray." (Of course if Pussy had not gone AWOL in Season 1 and been under serious suspicion ever since then, I think Tony would have upped him rather than Paulie. Not that Paulie's slightly nuts or anything )

So I think Silvio is officially consiglere, as soon as Junior is imprisoned at end of Season 1 - when Tony becomes the boss.

But I could be wrong.

(P.S - Sorry about the long answer)