Interesting definition. I would have said what it's sold for doesn't matter at all when we're taking about whether it's fit for some arbitrary purpose.

I want to probe your definition a bit. Let's say a factory makes gears. All the broken ones get recycled. After all quality checks have been done, some of the passing gears are pulled off the line and redirected to the gift shop to be sold as paperweights.

1. Are unsold gears in the factory storeroom fit for purpose as gears?

2. Are unsold gears in the gift shop fit for purpose as gears?

2a. If yes, do they lose that fit at the moment of sale?

2b. If no, do they regain that fit if the factory has production issues and brings a crate back from the gift shop to sell as gears?