There are three preorder themes that I am aware of:
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Sephiroth (Amazon preorder)
Cloud and Sephiroth (PSN preorder)
The theme for PS+ members is not the same as the PSN preorder theme; the PS+ one features Cloud and Midgar. Also, I think you're mixing up release dates; they haven't said when the PS+ theme will be released (just "soon"). The only one they've tweeted about that will be available April 10th is the one for the demo.