CREATE TABLE table_name_68 (date VARCHAR(255), result VARCHAR(255), location VARCHAR(255), year VARCHAR(255), loser VARCHAR(255))
Which date had a year under 1988, loser of Philadelphia Eagles, location of Giants Stadium, and a result of 21-0?
    
SQL: SELECT date FROM table_name_68 WHERE year < 1988 AND loser = "philadelphia eagles" AND location = "giants stadium" AND result = "21-0"