After all these posts, and confusion, you should have thought of it this way.
You were "Gold" at the beginning of your second cruise right? This is also spelled out on the Carnival site IIRC. So, you should be platinum at the beginning of your 10th cruise. Why would Carnival change the way they looked at your status for your 10th cruise, but not your 2nd one?
Congrats by the way, we are 1/2 way there :P
Western Caribbean - Elation - April, 2015
Southern Caribbean - Triumph - October, 2015
Exotic Western Caribbean - Dream (B2B) - November, 2013 (Our Honeymoon)
Eastern Caribbean - Dream (B2B) - November, 2013 (Our Wedding)
Mexician Riviera - Spirit - November, 2011
Western Caribbean - Freedom - January, 2011
Southern Caribbean - Miracle - November, 2010
Western Caribbean - Liberty - November, 2008
Eastern Caribbean - Valor - October, 2006