I'm trying to remember, aside from B-4, Lore, Data, Juliana Tanner and Lal, when did we ever meet three other Soong androids, since there's a scene where there are six holders, but I only recall those five androids, and with Data dead and Juliana Tanner elsewhere, why did the Daystrom Institute need three additional containers?
I think they're from Immortal Coil
, possibly based on something Julianna said in her TNG episode. Three unfinished prototypes, without humanoid features and which never achieved sentience. In my brain, they're B-1 through B-3.