It could, by someone who was willing to purchase a copy of the report (I'm pretty sure JPR would happily sell one), and
AFAIK so far no-one has actually put out an article using the real report that effectively refutes AMDs figures: probably because
AMD used the actual figures reported by JPR.
Let's face it - JPR are a big name corporate research body. If AMD were misinterpreting or misusing their figures to any significant extent, don't you think they'd have mentioned it themselves by now? If the figures are inaccurate and a third party gets a copy of the report and proves that it trashes JPR's reputation.
So actually, I think we do know that AMD's 83% of total addressable market is accurate. What we don't know if how JPR/AMD are defining "total addressable market". It's clearly not how the gaming press want to define it, but then <whisper>
the world is bigger than just computer gaming</whisper>...