Please see my post in Blatant Advertising.
https://permies.com/t/80/51274/Sunroots-Sale-Genetically-diverse-Prolifically#3569677
My sunroots produce seeds every year. (They require an unrelated pollinator, and I grow lots of different varieties.) Some years they yield more prolifically than others. The goldfinches act erratically from year to year. Some years they pounce on the seed heads early and consume them voraciously. Other years they mostly ignore the seeds. And the weather makes a difference.
This year, I pruned the sunroots when they reached chest high. That encouraged them to send out lots of side shoots, which made lots of seeds. Next year, I may aim for pruning them at belly height. This year they still grew over 7 feet tall, even with pruning.