You are right she has to use the chakra from the yin seal to transform it into a new seal in order to use Creation Rebirth or Byakugou.
You said it yourself, she released CHAKRA from the seal, not the entire seal itself. Tsunade can release chakra from that seal to increase the power of her attacks, but when she releases the entire seal she will enter hyakougou mode, which can only be done when you release all the chakra in the seal at once. See the difference now?
Sakura releasing a little chakra at a time to increase her punching power is not the same thing as releasing the seal itself.
The seal is meant to hold chakra, that's it, nothing more. When you release the seal you release the chakra inside of it. That is releasing the seal. Completely obvious as Sakura already stated she released it. If she didn't release the chakra in the seal she wouldn't have gotten a powerup.
Lmao, nope. Tsunade releases the seal, which then releases the chakra stored inside the seal. The chakra in there is used to activate Byakugo. Yin Seal Release=/=Byakugo. Byakugo is only used with the chakra in the seal. Byakugo is not directly caused by the release of the Yin Seal.
Is there a scan proving this? I always thought that those techniques used the chakra stored in the seal and thus were predicated on it.
The techs do use the chakra stored in them. IT doesn't mean that when ANYONE releases the seal, that those markings will appear.
The proof is Sakura. When she released her seal did markings appear on her body or her forehead? No.