Its nothing special and i dont see what these informations bring any advantage....
Its known that a lot of vintage and also actual quarries deliver products of a general use (roofing slate, garden pebbles, etc.). It was always needed to run a business...
Many of the quarries would not have operated sucessfully if they would not have sold these types of products.
German Slate was used for all types of Slate Products (like slate pencils and slate tiles) besides that it delivered good razor hones
Coticules are actually re-used for garden pebbles for decoration.
https://youtu.be/tYqMq4RmIvg
BBW is re-used for general purposes. As it is today used for sharpening razors and knives.
Vermont Slate is produced for slate tiles, on the other hand it can be well used for finishing razors
Welsh slate is used for roofing slates, slate tiles, adress signs, etc...so it is used for honing.