There are different conditions that produce seedless fruit:
1. Tree can set fruit without pollination, cross pollination will produce seeds, no other compatible variety is present to pollinate.
2. Tree can set fruit without pollination, other varieties present but the tree won't accept foreign pollen.
a. Flower has a genetic defect where the pollen won't reach the ovules.
b. Flower has a genetic defect and fails to recognize compatible pollen, rejects everything.
c. Other causes I don't know.
3. Other combinations I don't know.
#2a is the condition I think seedless kishu, gold nugget, etc., exhibit.
Your concern has always been on achieving #1, I think.