But seeing as we know there was an increase, it would seem the Daizenshuu is in error if it doesn't even mention Buff Buu.
Except Buff Buu was the one to absorb Dai Kaioshin. It wouldn't make sense for him to be talking about Pure Buu absorbing him, because he didn't. And like I said in my last post, that quote from Kaioshin was talking about the heart, not the power. He's saying that Buu's heart has returned to the way it was before he absorbed Dai Kaioshin. Buu was evil before he absorbed Dai Kaioshin, so now, he's returning to being evil again. The mention of power is referring to the initial drop. It doesn't say his power is returning to what it was before; it's saying Buu's heart is.
I still say that it's meant to refer to unaltered Kid Buu. It doesn't mention the increase here, it just says that he got weaker from absorbing Grand Kaioshin. Then again I'm more or less ignoring that cryptic line anyway, so it's a moot point...
My opinion of Fat Buu: I power scale by the meter, as if what Kaboom says is accurate then the meter really is an indicator of his power, as the power seems to be going directly to him (he won't be at full power if he's released without it being full). I go with the following for the three levels of Fatty:
Initial:
50%.
-Considered pretty strong and, judging by everyone's reactions, is probably stronger than Dabura. But Vegeta basically laughs him off and Gohan says that he can do pretty well against him as a SS2.
Power Up 1:
75%.
-Here he becomes much stronger, pwning SS2 Gohan and Dabura effortlessly. Goku and Vegeta consider him much more impressive, yet Goku still says that if they go at him as a team, they'll beat him for sure.
Power Up 2:
100%.
-Now he's now on a new, different level from the SS2s, to the point where Piccolo and Vegeta both say that it probably wouldn't even matter if Goku, Vegeta, and Gohan went at him at the same time. However, he's still clearly no match for SS3 Goku, even though the latter isn't putting out anywhere near full effort.
And then his power basically becomes Super Buu's right before he splits.
This seems to work out well with that's shown and looks nice and neat. For example, by my numbers:
SS2 Gohan- 6,100,000,000
SS2 Goku- 8,100,000,000
SS2 Majin Vegeta- 8,400,000,000
Fat Buu-
--Initial- 6,500,000,000
--Power Up 1- 9,750,000,000
--Power Up 2- 13,000,000,000