Demandred's alter ego has not been seen on screen. (See link—particularly the footnote—because I get tired of writing it all out. :p )

Also, the Forsaken Garden Club meeting is good evidence that Demandred has been using the Ways to move Shadowspawn. He didn't send the 100,000 against Rand—it was the mention of the orders that made Demandred hedge, not the initial mention of Sammael's "return", and I'm sure Demandred would have avoided contradicting his judgment if possible—but he has been using them for something, and he knew that Moridin was likely to be suspicious of him for that reason. It's possible he was able to stockpile Shadowspawn in various uninhabited areas, since moving them through the Ways all at once is impractical at best.