It's not a dark prophecy. It was a "fail safe" of the Wheel in case Rand fell into darkness for good, lost himself and had to be removed from the Pattern as the last hope to defeat the Shadow.

The whole thing disserved the Shadow in the end, because for some reason they didn't put the efforts necessary to manipulate the Bordermen into a bloodbath. They either waited too long, or what they had planned just fell through. It's very obvious the Shadow wasn't involved in the decision of the four rulers, and they managed to keep secret the real reason they were going south with such a huge army.

Of course the Shadow would have contemplated the notion to use all this to get a bloodbath, most likely when the Bordermen entered Andor they could get embroiled in a huge battle there, but Elayne kind of ruined all their chances to organize this, this aside from the fact the Shadow obviously didn't want the Bordemen to come near the BT at this delicate "endgame" juncture. It appears, we can surmise from hints regarding Shiaine's orders from Moridin, that the Shadow just cared to delay and weaken Elayne's position, and really divide Andoran Houses before they let Elayne take the throne. The plans were long in place to "take care" of Caemlyn (the ones Verin heard about), it didn't matter who held the throne, and Elayne actually would give the Light a false feeling of victory and order.. before the big attack destroyed that. Another advantage was the fact the succession kept the armies of Andor all around Caemlyn but out of the wall and looking at the city.... The Shadow attacked one city... from the inside, and dealt with the core of the biggest national force in the land, beside holding the city at the very center of the Land, isolating TV.

In any case, all that aside, Elayne captured the BA and Moridin's agent who was pulling the strings of some of the Houses assieging the city and opposing Elayne. It was no longer a possibility to influence some Houses to go after the Bordermen, and it would hav taken a huge army to really bloody the Bordermen anyway. The Shadow must have just dithered.. there was nothing obvious around to take care of them. I highly doubt the Shadow is behind Roedran.. the best use of the Murandians would have been to send them against the Bordermen at Far Madding... What remained? Semirhage pushing Tuon to attack FM and the Bordermen, which would have bloodied both sides. But Semirhage and the really influencial agent of the Shadow near Tuon were out of the game, Tuon missing for a long time, Mat and Perrin distracting the Seanchan and no doubt slowing a little their plans to move north.

So no option left, the Shadow was screwed. They had to leave the Bordermen be for the time being, they'd be destroyed during TG.

Their departure appeared to be a good thing for the Shadow, but they have left enough back home to fight anything short of the TW coming again. The Shadow has more than enough to overrun the Borderlands. Had the armies and rulers been home, they would have attacked even more strongly, and probaly moved to kill some of the key players, great generals, rulers etc. The Shadow had a plan to invade all the nations at once, preventing them from assembling to block Tarwyn Gap. Shienar can't hold it very long alone, but Saldaea, Kandor, Arafel were caught with their own invasion so... In the end, without the four rulers and a massive army going south, the Shadow's initial attack would have been a bit more difficult, but also far more devasting, leaving scattered and tired forces to hold the Shadowspawn at Tarwyn Gap. Now the rulers are re united to the forces going to Merrilor, they have their best generals with them, and that opened the path for Lan to gather a huge army to bring it to Tarwyn Gap. Meanwhile, Rand moved to help at the Blight, and sent Asha'man, worth even more than the armies that went south...

It's a costly win for the Light, but it's still the Light that benefits the most, purely accidentally of course, from the rulers going south.

The Shadow could have turned this into a devastating mistake, but opportunities never opened. Elayne's plans put the Bordermen on their guard. They knew she intended to use them as a threat with which to bring the Houses behind her and win the throne. That made them massively careful in how they moved, going way east of Caemlyn and slowly, until they were sure the assieging armies remained at Caemlyn, after which they rushed through the Hills of Kintara to Far Madding, avoiding Lugard too. They chose Far Madding because they needed to feed their armies, and because they could either reach an agreement with the merchant-rulers there or if they failed this central trade hub didn't have any army with which to threaten them or oppose their presence. All the other choices were bad... Lugard/Murandy, with its feuding lords and weak King. The Seanchan in Altara, Illian and Tear too far and held by armies of Rand. Then there was the Guardian as a bonus, probably an extra the AS with them pointed out, but not the primary reason to stay in Far Madding, the ideal place for them to send envoys to find Rand and ask him to come to them for a meeting. The meeting that originally they hoped would have taken place many months before at the northern border of Andor and when there was no sign of a winter coming. They had hoped to have to cross only the Black Hills with that huge army, meet Rand, deal with him if necessary, and return home.


-----

Dark Prophecies are something else.

Since Sanderson confirmed Moridin is like Egwene a Dreamer(well, it's down to either him or Demandred, it's an easy guess to make it's Moridin), it's fairly obvious where the Dark Prophecies come from.

They have to be Moridin's own Prophetic Dreams, which he describes in grand pompous style to make them sound like Foretelling, foretelling that praise the Dark One.. because Moridin phrase them this way. But all the predictions are from his own Dreams, they're probabilities rather than absolute prophecies like Foretelling or Viewing.

He must keep most of them for himself as if a notebook to plan his moves (in the book Perrin saw Lanfear spying on in TAR, I'm pretty sure - it's the same he showed Graendal in TOM), but also uses them for propaganda or as threats when it's useful. He probably leaks among DF some of those that have come true, to increase their faith in those he leaks as propaganda.

He referred to the DP and his dreams (I think that's what he was alluding to) in TGH. He told his DF he foresaw many nexus in the Pattern coming where events could be turned in their favor, and if it failed, there was more of those coming. That's what Moridin is aiming to do with his Dreaming, find those points where it's possible to make things turn in the Shadow's favor, sending the Pattern off its course. Those nexus he's found in his Dreams, that's what he writes down as Dark Prophecies, IMO.

Calling Rand "First Among Vermins",Mat "One-Eyed Fool". That's classic Moridin/Ishamael.

When you think about it, little else makes sense as sources for the Dark Prophecies. "Dark Foretellers" would be Black Ajah, and extremely rare. They would not control their foretelling, for one thing, when and in front of whom etc. and Ishamael would have no way to collect those, no more than he could with any ease collect Dark Prophecies during the Breaking or anything like that. If a BA started to pull an Elaida or Nicola and spouted stuff à la "The Great Lord of the Dark shall bring us the Darkness so beautiful" in front of anyone, she wouldn't have lasted long... it would have been a race between BA and non-BA to execute her.

Perhaps, "prophecy" was a bad choice of words. It is really the testing of Rand by the Borderlander Leaders that I found to be a very weak plot device. It seems rather lame that the Dragon Reborn would be deemed worthy of that title by knowing of the existence of and name of a clerk. That along with the slapping of Rand just did not ring authentic to me.