Didn't it say in the back of the book that all the orders of knights radiant were tied to a specific type of spren? And I guess there could be surgebinders besides the knights but the knights seem to pretty completely be the main ones.
Also, it seems like too much of a coincidence that Szeth has like the most absurdly huge sense of honor, and has the powers that come from bonding with honorspren, for him to not have genuinely bonded at some point. And, if there's always a truthless, what could ever be the point of that (considering that Szeth appears to have been traded away almost immediately after becoming truthless, or at least the guy who traded him wanted to get rid of him so badly that he wouldn't accept payment/threw out what he was given). My theory is that Szeth got his honorspren before he became truthless and now it's like WTF because he's killing people. Or it might be in a morality crisis because his honor is at odds with logical morality, or his spren was trapped in his oathstone as part of his punishment.
My personal theory is yeah, Szeth was a warrior, got traded among people, was picked to have a shardblade, was super honorable, got his spren, followed some ancient traditional command regarding voidbringers, got punished with his spren imprisoned (thus freezing his powers and the spren's sentience at their levels from the time of punishment) and was sent into the world as truthless.
On a side note (I know this is the wrong thread but it will take someone like two seconds to answer) what is the second number in Posts: number out of number. In Brandon's like FAQ he says he's going to explain the levels but as I remember the answer is mysteriously missing.