999 

 Why did people code their missing values as real numbers such as 999 in the old days?  Why not “." from the get go?  And why do many big, federally funded surveys insist on numerical missing values to this day? 

 Don’t we all have stories about how funny missing value codes (“-8") got people in trouble (think The Bell Curve)?  Are there any anecdotes where people got in trouble for mistaking “." for a legitimate observation?