It's a good question ... (although, was it rhetorical?)
I can only remember one game at The Amex where I think there was no added time.
What is the time being added for? There is regularly "a minimum of (3 or 4) minutes of added time" when the game has had no stoppages or delays. And there is ALWAYS 1 extra minute on the end of the first half.
They might as well make the first half 46 minutes.
My season tickets at The Amex are almost opposite the technical area, and we can see the guy holding the lit-up board with the extra time on it, before he walks to the touchline and holds it up.
To borrow a phrase from one of your chaps, TTT ... It is a riddle, wrapped in a mystery, inside an enigma.