Well not fair (If I am not mistaken)

[Moon Helldiver]

Ascent and Descent. I forgot to pick up Prismatic Fragments during post campaign story missions. I did not even know there were Fragments. Now after I already played them... the only chance to get them is to play the same mission on light level 2000... while I am 1960. What I am missing? How can I start those on normal, or I have to grind my self up

[Eradrazil]

If you finished the campaign on Normal, then just go to the campaign button on the Pale Heart director and select the appropriate missions. If you finished the campaign on Legendary, it fully unlocks it on Normal as well.