The Papa Song character, implied to be Ronald McDonald in the book, was changed to resemble a smiling, rotund yellow Buddha-like figure in the film. Becomes brilliance when you realize that (as described in the book) Sonmi is directly compared to the original living Buddha in that she was a real human being who achieved fame for her compassionate humanistic teachings during her relatively brief life, but became deified beyond belief by civilization after her death to the point where her worshipers are largely unaware she was ever a flesh-and-blood human, so she's a satisfying antithesis to the corporation's soulless bastardization of the Buddha's image.
Sonmi~451 mentions reading Huxley and Orwell. Brave New World, as said on the regular page, is referenced almost completely, but the twist she reveals at the end, that the resistance was a set up by the actual people in power, is straight from 1984.
After the reveal about Soap, Sonmi later mentions that she's jealous that fabricants are incapable of eating human food. She knows what Soap is and she is physically unable to eat anything else.
Sonmi~451's decision to become a prophet of sorts comes after she is shown the fabricant recycling facility. Her words eventually become the scripture of Zachry's era... but people per se haven't stopped eating each other; in fact those that do are much more blatant about it.
How does Luisa Rey know about the Cloud Atlas Sextet when she only got the letters Sixsmith had been rereading — the first nine, the ones we've just read, that don't mention the sextet yet (nor that he published anything)?
The only explanation I have for that is the whole "Oh, I'm remembering that I used to be this guy" thing. But yeah, good point.
Luisa is a reporter who (one can assume) is used to digging up information on people. Reading a stack of letters from an composer from just 40 years prior is more than enough information to hit the library with. Since it seems like Frobisher didn't compose a whole lot that survived the decades, the Sextet is probably the only piece of music by him that she can find (most likely as a footnote in a book about Vyvyan or something).
But in the book, she isn't remembering yet, and Ayrs probably made sure Frobischer was almost unknown. It's possible, I suppose, but not self-explanatory... Guess it can join the list of plot-related oddities that might be deliberate and throw a doubt on whether anything is real (along with Luisa's story being a book and her lifespan overlapping with Cavendish's).
I thought this was pretty obvious and easily explainable: When Luisa reads that Frobisher is a composer, she calls a few old record stores and asks if they have any works by Frobisher. The guy at this record store must have called her back (because he probably wouldn't have known of the top of his head) and said "Yes, we have the 'Cloud Atlas Sextet'" and so Luisa goes to get it. The record store clerk does say that after they spoke, he pulled out the record to make sure there were no scratches. Maybe a rather mundane explanation when the rest of the stories are so fantastical, but that made the most sense to me.