Do old CRT TVs and monitors distort their image, or cut it off?
CRTs were originally round, as can be seen in this 1945 prototype. The cabinet masks off the outer parts of the tube to create the square viewing area. This is called overscan. Later tubes were more rectangular, but still relied on overscan. This was partly because as the tube aged, the scanned area shrank, so the cabinet would hide the blank parts of the screen. The front to back curvature of the tube is not accounted for in the image because every model tube had a different curvature and I don't think it added much distortion.

Curves at the rounded corners of the cabinet were also not accounted for because of the differences in cabinet. But that was part of the motivation for overscanning and for limiting important picture elements to safe areas.