(re: Derek Karlavegan??)
If I remember correctly (and someone will correct me if I’m wrong), Derek K. first appeared in the KQ6 manual. That means that his identity at least was created by Roberta / the KQ6 design team and supported by Roberta. As for the general creativity and add-ons by Spear, I myself wouldn’t treat it as canon Sierra material – but as the guides are authorized by Sierra, well, I guess you can consider them semi-supported by the designers. Isn’t there a quote from Roberta on the KQ companions? I’m at work so I can’t check right now. They are interesting books, though I don’t always like Spear’s writing or concepts.