It's possible that there is only one slug, and they're only summoning parts of it, as opposed to the entire thing. It is an interesting difference.
Originally Posted by aggeroff
On a different note, I wonder, has Sasuke expanded his plans from just destroying the Leaf Village, to destroying all the villages? Removing the bijuu would weaken the villages, plus how the bijuu and their vessels were treated by their respective villages was emblematic of the problems with the village system.