Oh yeah, he could spin a tale, and for WOT itself we caught him at it once (or rather Maria did) when he totally invented an explanation about Elaida and Siuan, not remembering what the real back story was.

But in Q&A he seemed more cautious and to RAFO what he wasn't too sure of (which apparently wasn't much... a lot of people mentionned RJ's amazing memory of his story's details)

About Taimandred, my impression is that he didn't lie. I always believed Jordan's intent with Taim was to give him what he thought were subtle enough overtones of Demandred. Taim in some ways is a plain replay of the Demandred - LTT back story. He kept doing that through LOC (subtle stuff, like Barid Bel Medar resenting LTT even more for the honors he showered on him etc.).

I think he was surprised that wasn't nearly subtle enough and that it gave rise to Taimandred. He stopped doing that in the next book, putting those parallels to BBM's bio in Taim's story. One of the last instances I remember is Taim leering at Elayne.