No PORT in a storm
Years ago, I worked for a well known decision support software company where the MD took pride in using their own software tool to query data, produce charts and track the business. One of his key data sources was the spreadsheet updated by the Finance team on the shared network drive of all customer shipments so the MD could keep his finger on the pulse.
Being a curious database man, I looked at the underlying data and my eye was drawn to the Port column which had entries such as "Win", "Windows 3.1", "Unix", and also lots of what seemed to be random letters, which I thought a bit strange. Later, stood in the MD's office while he brought up some of his charts and drew some conclusions, I saw him enter the letter "P" as a parameter for the column in his query, so asked him what the Port column was supposed to be.
"Ah" he said, smiling in his condescending style "If you'd been here since I started the company, you would know it's not 'Port', it's 'P or T' - Production or Trial and I only want to track the Production customers, not those who are only trialling the software".
Obviously that information was also news to most of the Finance team who had been entering the data based on their assumption of 'Port' for many years! :-)
As they say, Garbage In Garbage Out.