Originally Posted by DiapDealer
Just a bit of clarification. To my knowledge, uploaded mobi/prc files are not further "converted" by the KDP process. Since kindlegen (& Previewer) now produce a file that contains both the old MOBI format and the new KF8 format. Amazon will split the file into it's separate components so that they can deliver the proper format to the proper device (they don't deliver the whole uploaded file) and they strip the source from it (if it exists) before they deliver to customers. But otherwise, they're delivering the exact same mobi you uploaded to them.
EDIT: that's with kindlegen-produced MOBIs. I have no idea what, if anything, happens to calibre-produced mobis.
Diapdealer, thank you for these additional comments. FYI, I haven't enjoyed working with Kindlegen, due to their cryptic errors. Calibre is free (they ask for a donation, which I'm going to give them soon), but it is a Universal format <--> format converter, which has a nice Windows interface, and is quite intuitive. Also, I can build all my book formats for all platforms, from this one platform, which I find useful. Lots of useful 3rd-party add-ons as well. The only thing I don't like about Calibre is their adjunct e-Reader, which doesn't render all that well, but it is certainly better than nothing.