To get pedantic if we're going with what a black hole means and how it might apply in this scenario, we can "see" black holes across the cosmos. Hawking's theory about them emitting radiation into the universe, and therefore being detectable, is true.
It tends to align with my idea of a black hole collection. You may not know what's there, but you know it exists and may have an inkling of what's gone in, but for all practical purposes you can't be sure what exactly is in there.
So I'd include pieces that are shown on CAF and elsewhere, even if the owner has no intention of ever parting with them. Consider that the emitted radioactive particle proving the black hole's existing.