"I swore an oath to slay the betrayer of your father," Gurney said. "Do you think I can forget the
man who rescued me from a Harkonnen slave pit, gave me freedom, life, and honor ... gave me
friendship, a thing I prized above all else? I have his betrayer under my knife. No one can stop me from --"
Silly Gurney. Little does he know that Duke Leto did not rescue him from a Harkonnen slave pit. Gurney rescued himself and then joined up with a gang of smugglers, as portrayed in the book House Harkonnen.
Why would Gurney lie to Paul and Jessica about this? Both have truth sense and would instantly know that Gurney just lied about something that makes no sense to lie bout. Neither comment, of course.
The alternative is that Gurney can't remember his own personal history. Or something.
I'm sure Brian Herbert and Kevin J Anderson are both perfectly nice people that meant well to write more Dune fiction. But could we at least try to avoid, at the very very least, obvious continuity errors? Is that really too much to ask?