Kirin uses little chakra and harnesses pure lightning from clouds.
How the **** is he using Kirin?
I never said it was unknown. just that kishi didn't think Kirin through or develop it until around the fight with Itachi.
Given how Kirin is used and it's requirements. You're basically saying he can summon storm clouds at will or pull Kirin off with his own chakra, contradicting what Kirin is.
Kirin doesn't harness lightning from clouds out of necessity.
Sasuke was insanely low on chakra after using Orochimaru's signature substitution. In order to still use the attack and end Itachi's life once and for all, Sasuke decided to improvise by shooting two fire techniques into the air and use a minimum amount of chakra to tame and control the lightning attack so he could kill Itachi.
The manga doesn't state that Sasuke must use real lightning, Black Zetsu merely notes that Sasuke is using real lightning for this attack for obvious reasons; low chakra. Sasuke was incredibly fresh when Team 7 hunted him down in the hideout, eliminating the need to use actual lightning.
You can't bring up one scan saying he HAS to use real lightning because he doesn't. Kirin has no plotholes.