Many things in the early books were retconned in later books. Elfangor was allowed to project images somehow, but Ax can't. Later on that ability is given to Leerans, as their version of thought speech. You can find a list of KASUs somewhere, but the list isn't always accurate. For instance, Buffy running on a Thursday is considered a KASU, despite Buffy reruns really airing on Thursdays at one point. Then there's the one in book 11 when Jake is worried the snake poison will effect him after he demorphs. Someone claimed it's a KASU because bug spray didn't effect him after he demorphed in an earlier book, despite the fact that bug spray on your skin can't kill you. Snake venom in your blood can.
Anyway, you may want to look up the list of KASUs.