Well, this is how I see the things:
If I was to write a PhD thesis for example. Imagine that in order to write it, some parts of my thesis are based on my previous research that had been previously published either in some articles or in my previous thesis. Needless to say that those parts would be essential to my new thesis.
So in order to avoid self-plagiarism, I normally should give reference, hence credit these essential parts of my previous parts of the thesis and research even if I was the initial author.
If the university asks me for copyright authorization to use my research by others, despite having copyright authorization, they ought to give credit if they use essential parts of my research.
Assuming some people had read my thesis (including myself of course), and they/I didn't quote me/myself, or they/I just paraphrased me/myself in order to prove a different point of view than what had been written in the thesis, then it wouldn't have been considered as (self-)plagiarism, but probably as "fair use". However, in the credits, they/I would have been supposed to duly credit me/myself despite the copyright authorization.
In the music scenario case, if I am not mistaken, it is similar. Despite copyright owner's authorization, it is illegal to use/re-use previous parts of officially published work without credits, even if there's "fair use", as in many hip hop songs for example.
My main concern is that MJ's previous parts of songs have been used to create a new one. It is true that in the case of "Take Me Away", its creator didn't have the copyright authorization, but that was not the only issue. The issue is that if he had had the copyright authorization, he would have been obliged to credit all the essential parts that allowed the song to be created. So it's a credit related issue too.
Hence, this leads me to the fact that we have clearly identified copy-pastes from Invincible in the middle of the sentences on the Cascio songs in order to fabricate a new sentence. I am not questioning whether the copyright authorization is given or not, as I assume it probably is, since the songs are officially released and labeled. I am questioning whether Branca was aware of the sentences fabrication with copy-pastes in the middle of the sentences (not ad-libs), because they haven't been credited at all, yet at the same time those copy-pasted bits of sentences from Invincible are so essential that the new sentence on the Cascio songs wouldn't have existed.
To me this case is similar to including in my thesis essential bits from my previously copyrighted and officially published work without which my new thesis wouldn't be possible, yet without crediting it. Which means that it would be considered as self-plagiarism. Regarding (self-)plagiarism in general, there is no minimal number of words, notes, etc. as long as it is clearly established what comes from where and when it is not duly credited.
IMO, a seriously done work should be duly credited not only for legal reasons, which is obviously understandable and as a matter of fact an obligation, but also for the ethics out of respect for the initial work without which the new one wouldn't be possible, and also, why not, for the sake of transparency.
So, either Branca is unaware of this, because it's been hidden to him (as to us since not credited), or he was aware and thought nobody would notice it. But if this latter was the case, why taking such a risk?