My mini-series of hints and tips from past decades would not be complete without a contribution from the SAS-L mailing list - the 25 years old list server that continues to provide immense value to SAS practitioners worldwide. Joined by the comp.soft-sys.sas newsgroup in 1993, these two services have worked hand-in-hand to answer questions and share SAS knowledge.
Matthew Healy's 1996 contribution to SAS-L, entitled "Coding Missing Values", offers timeless advice for data model design.