That's not quite the impression I got from various interviews or the signing I attended.

Brandon and Harriet have been saying that RJ left huge story gaps to fill. For some characters he had nothing more than a first and a last scene in the book, others had a bit more as they resurfaced in the middle for some scenes - but Brandon had to invent them a story in between, using notes in the character's file (there were often options in there, apparently. Brandon had to pick one) or sometimes just his imagination because RJ left nothing useful. At the signing I attended, Brandon was saying that RJ seemed to have written key scenes first (and he worked completely out of order, that was his method), but not to be mistaken about that because what RJ considered key scenes are most often not what the readers would think of as "key scenes", like big action sequence or resolution. For RJ they were more about important character development moments than the plot, and for many such key scenes he left only a complete dialogue. Sometimes there were notes where the dialogue was meant to go (eg: location, or setting or a specific place or moment in the action) but often there was no context and Brandon had to figure out/decide where in the plot those dialogues ought to go. Brandon also said the outline had Rand and Egwene fairly mapped out (that's why he began with them), sometimes in details, but that for most of the others there were huge gaps. What RJ left about Mat (that we have so far read, that is - Brandon left no clue for upcoming stuff) focussed on the ToG episode. He left early Perrin/Faile scenes (the material that ended up in the prologue, also the Galad POV), but not much afterward apparently, and virtually nothing very concrete for Elayne's storyline Brandon has once hinted.

I wouldn't be surprised RJ left nothing at all for Aran'gar beside information about her demise. He doesn't appear to have left much if any details about Graendal either - at least the way she seems almost absent from Rand's storyline in TGS strongly suggest Brandon had not much details he could play with (if there were, he would have used them, he tries to discard nothing for which RJ had left notes on his intents)