Scott 2005 Standard Postage Stamp Catalogue, Vol. 6: Countries of the World, S0-Z (Scott Standard Postage Stamp Catalogue Vol 6 So-Z) 
asked by shawn on November 23, 2006 2:43 AM
23,000 value changes were recorded in Volume 6 with stamps of the Spanish area leading the way. Other countries with an extensive number of changes include Tonga, Uruguay, Switzerland, Syria, Venezuela and Sweden.