The fact that the stereo image could only be viewed correctly from a narrow viewing "zone" was the fundamental drawback of parallax stereograms. Excessive side-to-side movement of the head outside the zone would cause the left and right eye views to be switched and be seen by the inappropriate eye. The result of which was a pseudoscopic image where the depth is inverted (foreground appears to be the background and vice versa).
This problem of pseudoscopic zones was resolved for the most part by adding multiple views beyond the two stereo views for a wider range of viewing. This adds a "look around" capability, where the picture moves through a sequence of stereo views as the viewer moves from side to side, revealing different aspects of an object or scene.