I have been told by my OUTSTANDING TA that upgrades are a luck of the draw. A lot depends on when the cruise was booked, what category you booked, and was a guarantee and if you have been a past member of the cruise line, although at one time I had never cruised on one particular line and still I was upgraded.
On my last cruise a few weeks ago I was upgraded 6 categories from a cheap balcony to
a FULL SUITE, 528 sq ft of luxury.
E-mail me at firstname.lastname@example.org
if you want to now how I accomplished this.