Is this is how things actually work? I was under the impression that once you use a code the system won't let you use "previous" codes, and move on to generate

Is this is how things actually work? I was under the impression that once you use a code the system won't let you use "previous" codes, and move on to generate the next set. Edit: Found this: No codes are ever repeated, and once the alternating signal -- like, locking an unlocked door -- has been released, all previous codes are invalidated, which is intended to be a fool-proof safeguard. RollJam, though, hacks the process: hidden near a car or in a garage, RollJam 'jams' a signal with a radio, blasting noise on a common frequency used by automobiles, while another radio captures the rolling code. A user will press the fob again, thinking the device hasn't performed the intended function, and RollJam simultaneously captures the second code while releasing the first one -- the car is now locked, but RollJam has the second code needed to unlock the vehicle.