charliegolf, see PMs.
As A2QFI says, some ships are turkeys.
When are you considering going as when to book is the biggie. Booking early gets you big onboard credit and lowest prices. Booking late gets you bigger onboard credit and lower prices. Well that is what it looks like.
Late booking also gets fuel surcharges, less choice of cabin grade and position and limited dining options.
Readers Travel in the papers is also an excellent cheap route to late booking.