PlayStation Development Network

This currently doesn't make any sense to me, can you explain what these are ?

Any sample file would be much appreciated.

Maybe it is a TIM that has image data at different bit depths. I'm not sure though as I've never heard the term mixed-mode TIMs before.

It's in File Format 47.pdf, I concluded that as well, I suppose they are 16-bit size pages to comply with the frame buffer.