Here's something not yet answered:

Referer = A
Referred (new toon) = B
Third account (not referred or referrer) = C

They note that if the mobs killed are gray to A or B, then triple xp won't happen. But what if A and B are the same level (new toons), and C is a level 70 boosting them? Do A and B earn triple xp? Or just B? Or neither?