context-dependent, or "reified" assertions are a pain point for sure. I come from the perspective of cultural heritage data, where context is king. Which expert made this attribution for this painting? Who owned it _when_? According to which archival document? etc.

Almost all the engineering problems cited in the original post are still basically there, but graphical models are still the least painful way of doing this, particularly when trying to share data between institutions. Example: https://linked.art/model/assertion/