Rime doesn't spawn some seeds despite having all the biomes

Dasha Saltvine and Oxyfern seeds aren't spawned in their respective biomes on Rime.

 I realized that the Rime is supposed to be devoid of life, but there should still be some seeds underground to uncover

update, I replaced entire Rime world with vacuum to see how many seeds it will get me and this are the totals:

As you can see, not a single Oxyfern or Saltvine seed