CREATE TABLE table_41912 ("Date" TEXT, "Cover model" TEXT, "Centerfold model" TEXT, "Interview subject" TEXT, "20 Questions" TEXT)

When was Shannon Long the Centerfold model?
SELECT "Date" FROM table_41912 WHERE "Centerfold model" = 'shannon long'
SELECT "Date" FROM "table_41912" WHERE "Centerfold model" = 'shannon long'