I once saw speakers at a scholarly meeting nearly come to blows over a discussion of provenience, patrons, and museum policy. Does showing an artifact with an unknown exact source give encouragement and a veneer of respectability to looters and those who buy from them? Or are some pieces important enough to show anyway? If an expedition is underwritten by a collector or patron who has acquired undocumented pieces in the past, is the work of that expedition tainted? And so on. Feelings ran high. Context is crucial in archaeology - unless you know the source of an item, you know little about it. Patronage has a long history in archaeology as well - expeditions are expensive. No easy answers. I know some museums, as a matter of fairly recent policy, do not show undocumented artifacts.