I just came off the Millenium and have completed 5 cruises with them.
I was told by the Celebrity Cruise Sales Agent to call RCI and tell them that I have my 5 completed cruises with Celebrity so I will automatically become a platinum member on RCL.
I have completed only 4 cruises with RCI.
The Clubs breakdown are:
RCI - Crown and Anchor
Gold - up to 5 (Celebrity Classic)
Platinum - completed 5 cruises up to 10 (Celebrity Select)
Diamond - completed 10 cruises to 24 (Celebrity Elite)
Diamond Plus - completed 24+
Celebrity - Captain's Club
Classic - up to 5 (RCI Gold)
Select - completed 5 up to 10 (RCI Platinum)
Elite - completed 10 or more (RCI Diamond)