I use guides, pricelists, tradelists; transfer of inventory lists and saleslists that go back more than 25 and 30 years. Very, very useful for me.. especially with rare material both illustrated and described when comparisons employed; of which most can be searched for on line. There is no end to their use except to find an up-to-date value which is true for any pricelist except something on the order of a graysheet or current online auction results ... I'd be interested in any published European pricelist or manufacturers' catalogs from years past.