The pans are three different sizes, yes — so they are all interchangeable within their respective palette/pans.

I haven’t tried to depot the mini palettes (bottom right in this photo) but I assume they are removable pans. Those are the smallest pan size.

The other 5-pan palettes pictured are the largest pan size; they are the same as many of the palettes in this image from 15-28 pan size. However, you’ll notice that on the left column, the bottom two 15-pan palettes are smaller than the ones above them. These are the “midi” sized palettes with the third pan size across the line.

The Metropolis palette (bottom of third column) is a midi palette as well.

So three pan sizes: mini, midi, and full…