On a página da AWOIAF para House Stark, diz o seguinte:
Rickon Stark is the current Lord.
Why is this so? The whole world believes Bran and Rickon are dead. If everyone thought that they were both dead, why would they consider Rickon as Lord Stark, not his elder brother Bran?
Spoilers para Uma dança com dragões:
Lord Davos meets with Lord Wyman Manderly. They discuss Stannis' claim to the throne and what support Stannis might expect from White Harbor.
There is discontent in the North with the Boltons, the agents of the Lannisters, and Davos hopes to capitalise on this.
It becomes apparent that Manderly has learned from Wex Pyke, a survivor of the Sack of Winterfell, that Rickon and Shaggydog are alive - and that they have gone east to the isle of Skagos.
Manderley requests that Davos go to Skagos to bring them back to him - Rickon apparently being key to his plans to oust the Boltons, and he requests Davos do it for his known-skills as a smuggler:
"Roose Bolton has Lord Eddard’s daughter. To thwart him White Harbor must have Ned’s son… and the direwolf. The wolf will prove the boy is who we say he is, should the Dreadfort attempt to deny him. That is my price, Lord Davos. Smuggle me back my liege lord, and I will take Stannis Baratheon as my king."
Davos IV ADWD
So you can see the AWOIAF page is correct in-universe - as there are reports of Rickon being alive, but no reports of Bran being alive, Rickon is considered the Lord of House Stark (with Manderley claiming him as his liege lord).