On the NES, the system I'm most familiar with, the NTSC models produce 240 lines of video image, but the top and bottom 8 pixels are usually considered to be "hidden" due to overscan. (The actual number of hidden pixels varies along TVs from 4 to 12 it seems)
Most other systems at the time either have a similar issue or reduce the vertical resolution in order to show a consistent border colour in the overscan area.
I wonder if, by affecting the quirks of NTSC video timing, a 240 pixel tall image but where all lines are showing on most TVs is technically feasible. For example by making line rate as high as possible within the tolerance, and frame rate as low as possible, so that more lines can be squeezed in less time.
Does this even affect the overal heigth of the image, reducing the probability of lines being hidden by overscan?
Note: I do not count having two interlaced frames of 120 lines to be a valid solution.