Have been trying to decide whether a valid generalization can be made between derivative work which is specifically un-authorized, work for which the original
author never had the chance to authorize or not, and work the original author endorses.


I think there is a difference between author-endorsed work and internet fanfiction -- not in quality, but in . . . intent? flat-out authorial control, anyway. Fanfiction is often about pushing boundaries; tie-ins are by definition about staying very carefully inside them. Unless your John Ford's hilarious and sly Star Trek novel, How Much for Just the Planet.