1972 - the year Atari was incorporated.
Go at a nice steady rate, not too fast or slow, usually takes 2-3 tries before you get the speed down properly, then the secret Paddle Games Menu will appear, use the joystick, select which game, once loaded, plug in a pair of original Atari paddle controllers into the console and and press Reset (or select to select a variation, then Reset) to start a game.
Up once, down 9 times, up 7 times, down twice (1972).
The german Wikipedia article on the Flashback 2 states it's "Fire once, down 9 times, up 7 times, down twice"...
Does this work too or is this an error? If so, I would edit the Wikipedia article accordingly.