Getting Serious About Qualifiers

On several occasions I've mentioned the idea of adding qualifying events to my page on the World Chess Championship : Pre-FIDE Events. Posts where the idea came up are:

• Mikhail Ivanovich Chigorin (1850-1908) • 1890 Chigorin - Gunsberg, 1893 Chigorin - Tarrasch; 1889 New York
  
• More World Championship Qualifiers? • 1904 Cambridge Springs, 1927 New York, 1938 AVRO
  
• Groningen 1946: A World Championship Qualifier? • 1946 Groningen
  
• World Championship Qualifiers 1946 • 1946 Groningen, 1946 Prague

Other topics worth noting against 'Pre-FIDE Events' are:

• 1905+: Challenges to Lasker
  
• 1922: London rules
  
• 1927+: The Alekhine - Capablance return match, other challenges to Alekhine
  
• 1937: Euwe's attempt to transfer responsibility for the title to FIDE

Related topics already covered by other blog posts are:

• 1935+: The Botvinnik - Keres Rivalry
  
• 1938: The Club of Eight
  
• 1938: The Alekhine - Flohr Match
  
• 1945+: The World Championship Interregnum
  
• 1946+: The Interregnum According to Fine

Since it's not completely clear whether a particular event should be considered a qualifier, some criteria are necessary. One would be that the participants played with the expectation that success would bring an opportunity to compete in a match for the World Championship.