Normally MJ talked in between takes, numbled, humming etc. etc. - if all of that all of a sudden is missing from demo vocal tracks - he should have been alarmed... How could he allow it to happen??
It was discussed a few pages back that Eddie Cascio tried to claim that he 'had to free up space' on his hard drive, therefore deleting every single extra demo vocal off his hard drives. Of course, if you isolate just the vocal tracks of legitimate MJ songs, you can often hear Michael sometimes clicking, stomping or banging along during the vocal recordings. It's not a guarantee, but it was constant habit of Michaels that persisted on many, many tracks so even if what Cascio said about the hard drives was true (hint: it's not), you should still theoretically be able to hear those sort of noises
underneath the singing at least
sometimes!
So how were the Estate/Sony conned? Well, my theory is that Sony, Branca and McCain had no reason to disbelieve Cascio. On top of this, he was generous to hand over a number of late 'Michael Jackson' tracks when other artists who worked with Michael in his final years - such as will.i.am - were more reserved.
Alongside discussions and reasonings us fans will likely never know about, I don't imagine Branca and McCain are overly familiar with the audio post-production process and all the technicalities of it. I imagine if you were to tell them "Michael's voice has just been heavily processed because they're only rough demo vocals", it would be passable (hell back in the day, this reasoning satisfied me). As for the non-vocal noises MJ typically made on vocal takes, neither Branca nor McCain worked in the studio with Michael so they wouldn't be aware of this behaviour, which definitely goes against the norm of recording clean vocal takes. As such, the clean recordings of Breaking News, Monster and Keep Your Head Up wouldn't ring any alarm bells to those unfamiliar.
Teddy Riley is another story and I haven't a clue what he was up to.