I read the books in my own language, not in the original language, so it’s also possible that some of this comes from misunderstandings caused by translation.
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In the prologue of Elantris (10th Anniversary Edition), we see Hoid near the pool, with something that is described as similar to an Seon - but with distorted lines inside it. I thought this was the Spern that he bonded on Roshar.
But… someone reminded me that some of the characters from Elantris appear on Roshar, in the interludes, when they are searching for the stranger from the Purelake. They are Elantrians (I don’t remember which ones right now), so this would have to be after the fixing of Elantris.