Why oh why, don't any of these components just recognize the format from the disc when you load it?
The only component which knows the format of the disc is the player. After that only assumptions can be made. It is probably best to assume it is an anamorphic* image and stretch it to the screen, as that's most common format for recent releases. But as you've found that's wrong for older TV shows.
Modern upscaling DVD players do the right thing. They make everything into a 16:9 image (adding black bars to the left and right of 4:3 content) and scale it up to a 16:9 format (1280x720 or 1920x1080). That'll always display correctly.
*All DVDs have the same resolution picture 720x480, some store the image with a 33% vertical stretch, which needs to have the same amount of horizontal stretch applied by the display. If the display can't apply that stretch the player can be configured to reverse the vertical stretch before output (this loses 25% of the lines of resolution).
