Hi! Sorry for not answering earlier. If the museum in this case would go out of business I would tag it with was:tourism=museum or disused:tourism=museum or something similar. So I do understand the need for prefixes when there's multiple things being mapped with one map feature. However in this particular case I just don't see the ambiguity with the milk churn stands and find using the disused prefix with them more as unnecessary complicating things and stating the obvious. They have all been long disused in relation to their intial purpose so maybe the historic tag could be more appropriate? As a OSM data user (both professionally and as a hobbyist) I've got used to be prepared to query the data in many ways, but whenever it's possible to simplify notation without losing any relevant information I would go for it.