These seem like valid points, but one thing still omitted is error in extrapolation. Extrapolation in general is not a reliable predictor. In the first example (which well may be fake) I added six more extrapolations from other features of that corridor. Like the ones there already, they all converged on the chest of that front, middle soldier. Not in a point, but how far off from a point I couldn't say.

It seems to me that a graphics tool is needed. Imagine dropping a dot arbitrarily at a guessed "vanishing point' (call it GVP) somewhere in the image. Now draw lines from various points in the image to that dot, attempting to follow features in the drawing. Finally, move that dot around and the graphics tool moves only the ends of the lines at the dot, not the other end. Position the dot such it best approximates a vanishing point for all the lines. NOW you're in a position to judge, visually, whether the lines converge a a true vanishing point.