Hans Adam, Germany, 21 kills WWI, 12 kills WWII
Yoram Agmon, Isreal, 1 kill 6-day war, 4 kills Yom-Kippur war, 2 kills other Arab-Israeli wars
Takahide Aioi, IJNAF, 5 kills Sino-Japanese conflict, 5 kills WWII
Sada-aki Akamatsu, IJNAF, 11 kills Sino-Japanese conflict, 16 kills WWII
Bruno Alessandrini, Italy, 4 kills Spanich Civil War, 1 kill WWII
Qadri Al-Hamid, Egypt, 1 kill 6-day war, 3 kills Yom-Kippur war
Nilolai tyvich Alifnov, USSR, 5 kills Sino-Japanese conflict, 5 Kills WWII
Al-Zoabi, Syria, 1 kill 1982 war in Lebanon, 2 kills Yom-Kippur war
Marius Jean Paul Elzeard Ambrogi, France, 14 kills WWI, 1 kill WWII
And that is only going through 168 records out of over 11,000 air victory records. I'd say multi-war kills are fairly common ...