Was it ever confirmed that the slave Mindfang stole from Dualscar was Dolorosa, or is that just popular headcanon? And if it's confirmed, can I get a source?

Popular head canon because of the strong parallels between the slave and Kanaya. The romantic situation between Vriska and Kanaya then Mindfang and the slave. Dualscar killing the slave and Eridan killing Kanaya. Also on this page it says the Dolorosa was sold to seadwellers as a slave after the Signless was killed and Dualscar is a seadweller.