KH2 - How to tell which Gummi Ships I'm missing? (Figured it out)

[Ki11s0n3]

I've gotten an S in all normal missions and S in some EX versions and have both secret ships. From what I've seen ships come from normal missions.

Is there something I am missing?

Edit: In case anyone else is wondering why they aren't unlocking the achievement. I was missing the Invincible Peak ship. All I did was replay floating island mission 1 with Invinvible Rank 8 and got the item Material/Gx10 and when the mission finished I got the ship and achievement.