There is no expiration date on scientific data.  If you can find better studies, then that's great.  Unless you're talking about epidemiology work (e.g., how many people in which countries have this disease), then the age of the study is really quite unimportant.  Duesberg's 1988 "I think AIDS is caused by poppers" paper has significant historical interest, even if it was written before many WP readers were born.