CREATE TABLE table_204_983 (id DECIMAL, "year" DECIMAL, "1st venue" TEXT, "2nd venue" TEXT, "3rd venue" TEXT, "4th venue" TEXT, "5th venue" TEXT, "6th venue" TEXT)

which is the only year that mexico is on a venue
SELECT "year" FROM table_204_983 WHERE "2nd venue" = 'mexico city'
SELECT "year" FROM "table_204_983" WHERE "2nd venue" = 'mexico city'