While I can't recall who they were off the top of my head, someone correct me if I'm wrong, but you only get 10 more OPTIONS to start. They're not permanent unlocks. Once you create your first party of four, all the remaining characters get locked.
I played yesterday and had 24 characters to choose from at the beginning. After a few songs, I got red shards, and it gave me the option to unlock people I thought I already had. I was super confused at first, but when I went to edit party, I saw that there were only my chosen 4 plus the new unlock to choose from.
Oh, got it. Thanks!