What it sounds like then is there should be 10 separate threads for A Song of Ice and Fire in its various forms.
The TV show thread apparently can't mention that the books exist, even though the books are the source material and comparing them to the show is legitimate. But, posting about things that will happen in the books is a spoiler. And posting about things in the books that have happened is also allegedly a spoiler.
With that same logic, mention of the TV show shouldn't exist in the book thread at all since, while the books are currently ahead of the show, that may not always be the case and regardless, the books and show do vary, so posting about the show in the book thread would "spoil" the show for people who may not have seen it.
So, clearly, we need a thread dedicated to just comparing the books to the show, since neither the show thread nor the book thread can accommodate (using equivalent logic). That gives us 3 threads.
But in actuality someone who's only read some of the books or seen some of the seasons can't legitimately enter the show thread or the book thread, since that would "spoil" it. The only "equitable" result then is a thread for each season and a thread for each book. 5 books, 4 seasons plus a book/show comparison thread = 10 threads.
Anything less than that is a "spoiler!"