A generalization of the Pogorelov–Stocker theorem on complete developable surfaces

The well-known Pogorelov theorem stating the cylindricity of any $C^1$-smooth, complete, developable surface of bounded exterior curvature in $\mathbb R^3$ was generalized by Stocker to $C^2$-smooth surfaces with a more general notion of completeness. We extend Stocker's result to $C^1$-smooth surfaces being normal developable in the Burago–Shefel' sense.