CREATE TABLE table_4623 ("Year" FLOAT, "Competition" TEXT, "Venue" TEXT, "Position" TEXT, "Notes" TEXT)

Prior to 2004, what was the name of the competition that took place in Johannesburg, South Africa and had the 400 m hurdles event?
SELECT "Competition" FROM table_4623 WHERE "Notes" = '400 m hurdles' AND "Year" < '2004' AND "Venue" = 'johannesburg, south africa'
SELECT "Competition" FROM "table_4623" WHERE "Notes" = '400 m hurdles' AND "Venue" = 'johannesburg, south africa' AND "Year" < '2004'