In the heat of the moment, his mind racing, Asmodean popped into Demandred's mind only for him to think immediately, without an indication he pondered it seriously that "no, no... he could never have fought me like that".

That's hardly Demandred thinking Asmodean might have been a blademaster. It's more like Demandred struggling for a split second while in the Oneness to remember if Asmodean could use or not use a blade, only to conclude a second later that he would know if Asmodean could fight. It's not really so surprising that Demandred struggled for a second. Asmodean barely knew which end of a sword to hold, Demandred probably has no memory whatsoever of Asmodean related to swordmanship.

Demandred was always one to consider all possibilities rather than rejecting them out of hand. That's one way he avoids being blindfolded.

AOL arrogance aside, it's not so surprising Demandred considered a channeller either. To Demandred's eyes, Lan was clearly in the Oneness.

What's less believable is that Demandred, whom we know to have had spies near Rand, never heard from these spies about Lan Mandragoran, Rand's teacher for the sword.

That anyone from the late series' inner circle is a complete unknown to Demandred was surprising. Normally you'd expect Demandred to have taken a good look at Lan, who has quite a distinctive physique, and thought "That must be the famous Warder of that bitch who linked with LTT to cleanse saidin, the one who disappeared suddenly from LTT's circle". Lan isn't someone the likes of Elza would have forgotten to mention in her reports.

It's all the more surprising when you consider Demandred was convinced it was Rand sending him these men.