Metroid timeline is pretty weird. Originally, the Prime series was meant to fit between Metroid 2 and Super Metroid. However, as the Prime series developed and Sakamoto started fleshing out his vision of the Metroid storyline with Fusion and Other M, it's unclear if that's still the case or if we've fractured int separate Prime and Sakamoto timelines.
Weren't they between 1 and 2?
Which still works, btw.