Hi everyone! This is my first post, this is a pet thoery of mine I thought of while reading through SA. I was paying a lot of attention to numbers and their significance, and the lack of a 10th unmade really bothered me, so I tried to figure out what caused that discrepancy.
My theory is that the 10th unmade was held imprisoned the 4000 years Talanel was resisting Odium's torture. My thought is that each herald returning to braize did not hold ALL the unmade back, but only the unmade that corresponds with them. Taln's sacrifice did not hold all of the unmade at Bay - only the 10th. All reference to their being 10 unmade is lost, since the last desolation marked a new recorded history essentially.
I haven't done a full reread yet so I don't have specific examples, but this lines up with the levels of voidbinding, the incorrect histories, and just creates the symmetry that tends to exist in the cosmere. One counterpoint, maybe, is that Dalinar was supposed to be Odium's champion, which implies there isn't a 10th unmade.
Let me know what you think/ if there's an alternate explanation for why the numbers don't line up!