A bit OT, but I can see how someone can be led to believe that they are "sold as the same airline".
How could an unsuspecting traveler possibly guess that CX360 is a CX operated flight, whereas CX6869 will be on a KA plane?
They are not making it easier by sending out pre-flight reminders with a big fat Dragonair logo on it, for routes that are not even served by KA.
Until I figured out the 3/4 number code system on these routes, I had to hike hiking from one end of the check-in aisles to the other more than once
(why do they need to be so far apart, anyway?!)