I am not yet convinced fertilizing helps. I think its based on the grade of soil you use and then RNG. Like i have gotten 4 apricots from a harvest of Prickly Pine and Honey Lemon (fertilizing a 3-5x a day). And then last harvest when i fertilized as much as possible I got 3 seeds. And I did the same to my last Royal Kukuru harvest (I have gotten Royal Kukuru seeds from both Apricots and Honey Lemon before... as in harvested them from each plant) and got 4 seeds.
I have both beds running for glazenuts and they should be ready tonight or tomorrow. Have been fertilizing as much as possible so curious what I get. It may just be that you can multiples of the tier 3 seeds and not others (based on the fact that tier 3 seeds only give 1 plant per).