Ahh, the wonderful world of PAR (pixel aspect ratio). 320x200 tells you nothing
about the correct PAR. In order to obtain that, you need to know the dot clock
of the horizontal resolution for the video mode, to the TV/monitor. Then, you can tell what percentage of the active line 320 horizontal pixels represent. Only then can you get the correct PAR.
NTSC pixels are taller than they are wide...
NTSC has no horizontal pixels. The digital to analog device has pixels, but NTSC can show whatever 'resolution' from 1 pixel to 13.423mhz (13.5mhz is on the recent redefinition of NTSC since the digital era starting in the early 90's). The 'pixels' are only taller than they are wide, if the dot clock
is high enough.
Now which format were these games really intended to be played at? 4:3?
If the viewing device was 4:3, then yes. But you don't scale the 320x200 image to 320x240 or 320x256 or whatever. You pad the image. Of course, you need the correct PAR from the dot clock before you do anything.
Not only is this an advance topic, but graphic developers (well, game artists) tended to ignore correct PAR anyway. Which makes matters even worst. They also could have been working on an mis/un calibrated TV/monitor too