Do Daleks have gender?
How do they reproduce?
This Parliament recovered the massive Dalek Army the Doctor buried under all that molten ice on Spidiron?
So that's the idea behind this massive Dalek civilization, find the fallen, nurse them back to health until they can sic balls?
I mean with time travel, even time scoops at work, they can totally freejack all the lost causes they left for dead the first time around.