Latest word on the street is that AMD has not yet finalized PCB designs and driver integration for the Big navi cards, so previous performance rumors are probably pure speculation. Based on this new info, AMD could push the release schedule to October or even early November.
https://www.notebookcheck.net/Fresh-rumors-suggest-delayed-AMD-Big-Navi-GPU-launch-date-reveal-possible-VRAM-specs.482599.0.html
16GB out of 384bit bus? That does not compute, with that bus it's 12GB(12x8Gb), 24GB(12x16Gb) or 48GB(24x16Gb) of gddr6.
These are "leaks , someone just throws more or less accurate info. While I do not think that high-end card will use just 384bits. As you said it doesn't calculate.