@UDb23 You are referring to the concept of overscan. I think old CRTs often had slightly different borders where the image could be drawn. As a game builder, you maybe had exact specs on the monitor that would be used in the arcade cabinet, but best practice included placement of important items (like cockpit readouts, score text, etc.) within the "safe" area so that the image could be adjusted to fill the screen. Actually, the image may have been adjusted to go beyond the screen, ensuring all areas are covered. It's a bit like printing ink on paper using a full-bleed, knowing that the final piece will be cut such that your image goes edge-to-edge.
Anyway, I am glad you got it figured out.