Unless you normally take such jobs to a bike shop to be done then as a rider of bicycles you're going to have to do this sort of job at some point. I'd say that this is an excellent time to learn. Especially since they are still bare hubs and will be so easy to manipulate compared to having spokes and a rim on them.
Besides, you've obviously taken on the challenge of building your own wheels. You may as well learn how to clean and adjust the hubs.
And it's super easy to tell if they are NOS from a drawer or not. Look at the holes in the flanges. If the holes are smooth then they have never been built into a wheel. If they have small pressure marks in the holes and facing at alternating angles on each hole those are pressure marks from spokes. If you have such marks on the holes then they are NOT new