(Achievement) Can't find missing genes

[Werschaf]

Hello there,
I'm trying to get the achievement for completing the book of genes, but after hours of grinding I still can't find them. I have to admit, that I didn't completly understood how genes, shine and dens are influencing the outcome. Maybe someone can correct me?
I used the pot to increase the chance of finding rare genes and mainly searched super rare high rank dens(golden high rank).
I am missing:
1) 476 Inflict Ailment Gene (M)
Since I needed some other gene, I primarily farmed Nergigante in Super Rare High rank dens.
2) 528 Soul Kinship Gene (L)
Nergigante, Jho, Stygian Zinogre, at least 50 of each
3) Self-Heal Gene (L)
Nergigante again (the only one that is findable without coupons)
4) 616 Critical Kinship Gene (L)
Barioth, Legiana, Gammoth in High Rank Gold dens

I haven't tracked how long i've been grinding, but I found eight legendary dens while looking for these 4 genes.
So how does this work? Are M genes only in low rank dens?
And why cant I find one of the THREE nergigante genes?
Any help would be greatly appreciated!