Actually, the free cruise on Seabourn specifically is for a cruise in the suite you most frequently sail in; not in World's Leading Cruise Lines (Carnival owned cruise lines) cabins.
What that referred to was only Past Passenger Pricing; something that has pretty much disappeared. But if Seabourn does reinstate Past Passenger Pricing then WLCL past passengers are entitled to that benefit. I have had it applied many times.
I am still awaiting news on the revamped Seabourn past guest program. What I hear is that it is going to be very good.