The key is the wording as needed, as it's been made clear on this site and others, that before 1 second, the back may use a prior dark frame several times, and for sure the user doesn't see anything on the LCD, where as a 1 second or longer, the back shows the dark frame process being done each time, thus possible confusion. I will also assume that at 1 second or longer the back is taking a fresh dark frame each time, not reusing one since each time the photographer is not able to shoot again until the follow up dark frame processes. Also no buffering is used either to free up the back, something that IMO should be possible, at least by now with the CMOS backs, as Canon has figured out a way to process the dark frame in the background for years now. Eventually you will buffer out with Canon especially on longer exposures, but not on 1 sec to 20 seconds.
Paul C