A pair of mysteries established in the fifth and sixth Wheel of Time novels, published in 1993 and 1994 respectively, have been solved thanks to the actions of an eagle-eyed superfan.
WARNING: SPOILERS FOR THE WHEEL OF TIME NOVELS
In the fifth novel in the series, The Fires of Heaven, the character Asmodean is killed by a mysterious assailant. Robert Jordan did not reveal the identity of his killer before his death, but did include it in the notes for the novels. Brandon Sanderson revealed the identity of the killer as Graendal, a fellow member of the Forsaken, in the penultimate volume of the series, Towers of Midnight.
In the sixth volume, Lord of Chaos, Rand joins forces with Mazrim Taim, a false Dragon defeated in battle by the Saldaean army and taken prisoner by Aes Sedai. He escapes and allies himself with Rand, eventually becoming commander of the Asha'man. In the concluding volumes of the series it is revealed that Taim is a Darkfriend, sworn to the service of the Dark One. He corrupts a number of the Asha'man into fighting against Rand, but is killed by Egwene during in the Last Battle. However, fans doubted his true identity, citing a number of times when he seems bewildered by concepts in the world that someone should know and that Lews Therin Telamon (or, rather, his insane voice in Rand's head) seemed to recognise him. Fans concluded early on that he was probably the Forsaken Demandred in disguise. However, later novels showed Demandred and Taim in the same room and working together. The final volume of the series seems to confirm that Taim is exactly who he said he was all along.
Thanks to the efforts of superfan Terez, it has now been revealed the Robert Jordan played a bit fast and loose with fans. According to the voluminous notes he left behind, he did indeed intend Mazrim Taim to be Demandred in disguise, and that the disguised Taim/Demandred (dubbed "Taimandred" by fans) was also responsible for killing Asmodean. The former theory was already well advanced by fans at the time, but the latter theory was not. Robert Jordan had always said that the person who killed Asmodean had actually already appeared in the series, and neither Taim nor Demandred appeared until Lord of Chaos (although they were both referenced earlier).
Of course, the notes Robert Jordan created for the series were a work in progress and most of them were written during or after the writing of The Path of Daggers. By the time Robert Jordan started going online and interacting with fans regularly (after the release of Crossroads of Twilight in 2002), at which time he ruled out "Taimandred", he had changed his mind and decided that Graendal was behind the crime. This was helped by a popular fan theory published in the late 1990s that pinned Graendal as the murderer.
Although irrelevant now, it does show that writers, even major writers penning a series already many thousands of pages advanced, can change their ideas on the fly and adjust all the foreshadowing elements beforehand to fit a new idea if matches up to their designs more satisfyingly. And some old-school fans can take some satisfaction in knowing they were right, at least for a time.