Ok, one of the most intriguing questions regarding Sakura’s power-up was IF she had possessed this power all along (in her battle with Sasori, etc).
My answer is: YES! Now, it seems a bit complicated, right? Well, let me try to explain you properly why Sakura has been having all this power all along, but why didn’t she used it by now.
It all goes back to the recent enhancement she’s got, the Byakugou Seal.
As we know, Shizune tells us that for the past 3 years, Sakura has been storing chakra.
Friendly reminder, that we established by now that Sakura posesses the Byakugou Seal.
Now, a really important part here, is the part where Shizune tells us that Sakura has been constantly storing part of her chakra into that seal.
Which means, she hasn’t been adding that part of her chakra, whenever she build the chakra, into her punches so that’s why now, Sakura seems more powerful.
Let us remember how exactly Chakra Enhanced strength works.
As Kakashi reminds us here
Sakura builds up the maximum amount of chakra in her fist, then releases it in an instant.
So when Sakura said in the recent chapter that she can finally release her full power, she was referring that now, she can add how much chakra she wants in her punch, because now, since the Byakugou seal is formed, she doesn’t need to constantly put part of her chakra into the seal.
However, need I remind you that Sakura doesn’t use the chakra stored in her seal. The chakra she released in the chapter, was her own chakra, outside the seal!
How can we be sure of that? Well, as we know, the chakra inside the seal becomes usable when the seal is released, as we’ve seen with Tsunade.
Prime example, Tsunade’s Databook, Yin Seal Release.
Yin Seal: Release* (陰封印・解, Infuuin: Kai)
Fuuinjutsu, S-rank, Supplementary
Unravelling the key to using the “Genesis Rebirth”**!!
"Genesis Rebirth," the ultimate medical technique. However, using this technique requires such an enormous amount of chakra, that it is beyond any shinobi to mould it in an instant. Tsunade, using the chakra stock kept in the seal on her forehead, has cleared this prerequisite. With "Yin Seal: Release," the seal is released, becoming the source for the body regeneration technique.
[picture of Tsunade releasing the Yin Seal]
↑The moment it is unsealed, a pattern appears on the forehead.
[picture of Shizune preventing Tsunade from releasing the Yin Seal]
←Releasing the seal is the greatest danger signal.
*Kai (解) literally means “untie,” “unravel”.
**Genesis Rebirth (創造再生, Souzou Saisei).
So, as we’ve seen mentioned in Tsunade’s databook, the chakra inside the seal becomes usable when the seal is released. How can we tell? Simply, by the patterns that go around the body.
With Sakura, as we can see by now, the seal is unreleased.
So, yes, Sakura has been having that power all along, however, she hasn’t been using it because she needed to sacrifice that part of her chakra, for 3 years, in order to get the Byakugou Seal, which means, part of that chakra, didn’t go into the usual buid-up that Kakashi reminded us of earlier, therefore, her puches impact was less than the impact they have now.
But since now, she does possess the Byakugou Seal and doesn’t need to put that part of her chakra into the seal, Sakura can fully use all her chakra outside the seal, to make her punches even more powerful, run faster, etc.
Hope that is clear for you guys now, if not, I am waiting questions and I will try to answer them all for you.
Next question I will try to answer is the 3 years rule of the seal and if it will go away.
Hope the info was helpful!