For a collector of the Classics, a worldwide Classics catalogue is a valuable tool, as a prelude to using more specialized area catalogues if needed. The Scott 1840-1940 Classic Specialized Catalogue of Stamps & Covers was the first such catalogue issued, and it gets updated every year. It suffers from Scott's limitations related to its confused numbering scheme and refusal to list anything that was not used postally, but it is the predominant catalogue in North America.
There are 2 catalogues available from Europe: France's Yvert & Tellier's Classiques du Monde 1840-1940, a new resource introduced in 2010, and Germany's Michel's Klassik-Katalog Europa 1840-1900 which unfortunately covers only Europe to 1900. In my opinion, Michel publishes the best stamp catalogues both for their breadth and completeness of coverage and chronological numbering of stamps. It's unfortunate that Michel does not publish a worldwide Classics catalogue covering the period 1840 to at least 1940, if not 1950. Similarly, a worldwide Classics catalogue from Stanley Gibbons covering the period 1940 to 1952 would also be most welcomed!
The other option is to purchase older catalogues to cover the Classics period of interest from auctions, such as
ebay, but those don't have current values, although they do provide an idea of relative value.
Any other WW Classics catalogues or option that SCF members are aware of?