[shamanNS]

Swapping ASIN was done as experiment (like is it length of ASIN, is there a difference if it starts with Bxxxx,, does editing some other EXTH values like EBOK/PDOC help) in trying to figure out why books with fake ASIN (aka Calibre UUID) stopped having LPR sync option enabled in Kindle for Android app but the same files still work on Paperwhite. And there is only one possible conclusion in the end: sync is enabled only for books associated with your Amazon account.

As for your first question I didn't add same (non working but "not fake") ASIN to multiple books or the ones made by Calibre conversion. I've added ASIN from a book from my account to random Calibre converted file to confirm the suspicions. Method of elimination...