I am the Lead Product Designer at Nordnet, I will take your question.
It is an ongoing question for us. Currently, we have a workflow of a master UI Kit Sketch file where we maintain all our assets. That sketch file also gets implemented which is explained above as a part of the Atomic Design. Also, every project is handled in Zeplin, so we make sure the handoff is smooth and we can move fast. We can refer the items in Zeplin to UI Kit.
I hope it clarifies some of your questions.