Okay, wait. Maybe something here. Let me think; what happened to everybody. The Cult of Skaro was: Caan who went crazy/awesome, Sec who turned into Diagoras and was also awesome, the boring one that built the lightning rod, and the baby one, Jast. They all died in that dumb episode except for Caan, who went into the Time War and got Davros, and in so doing became an Abomination like Rose: Where she touched the whole of everything and became light, destroying her body, he saw everyone, the truth of war, and became shattered, like the Master (or Lazarus). Caan became beautiful and twisted, the only Dalek who ever laughed. He brought back only glimpses, like the written woman of Gallifrey.
Caan eventually sided with Sec, and was working behind the scenes all through Donna's year to bring everybody down. So these are just the weakest, palest children of the Cult of Skaro: The overly xeroxed grandchildren of Davros. That whole parallel Davros set up -- with the Children of Time on one side and Skaro's warriors on the other -- is what broke down when Donna died. So if just one remove away from Davros leads to this kind of miscegenation and self-doubt... No wonder Torchwood is so shitty at what they do! Jack Harkness is the Doctor's Caan! These guys are the Dalek Torchwood!
That's hilarious. Anyway. Somewhere in there the Dalek and Cybusmen had their little face-off, which would have been Torchwood, and Yvonne. Right? The Void. So then maybe came the cat-penises, and at some point there was Dalek Caan, who was like the most awesome, most wasted thing of all time; possibly involved in the above. And then they stole the planets, which is the thing Amy can't remember and the thing Adelaide couldn't forget. That's when Caan said all the crazy things, and Donna took care of it that time somehow, and they all piloted the TARDIS, which was cool. But who was left at that point, Dalek-wise? She was talking really fast and I don't remember what she did with them.
"One ship survived." Oh, well then. Okay. So they fell back through time, crippled and dying... and they "picked up a trace." One of their Progenitor devices, which is "our past... and our future" -- "That is deep for a Dalek," the Doctor says, which I guess is true but not exactly deep for anybody else -- and so the deal is that this Progenitor device contains pure Dalek DNA: "Thousands were created, all were lost. Save one."