Empty Seats? Yes please. Then Disappointment

On one flight from Singapore to Milan (Italy) several years ago, I asked at check-in whether the flight was full and was told no, there were seats available. Reason why I asked is when I booked my forward section seat in Economy I had a whole row to myself but then when I checked a day or so before departure someone took the window seat. I had the aisle seat and was hoping to score all three to myself. So I decided to change seats at check-in. By doing this I was wasting the money I spent for the forward section seat. No big deal as an empty row anywhere, even in the tail section, trumps a single forward section seat. The check-in agent...