Hi Steve,
I am not sure if you have found the solution to your problem, here are my two cents.
I have found this post by Tom_ where he goes in some details about what makes surface not-developable At the end there is a video that explains the ideas of flattening in detail. How to Unrolling doubly curved surfaces - #3 by Tom_
One way is to do the analysis of gaussian curvature. The tool in Rhino 7 is called CurvatureAnalysis, I do not know if it (and the commands mentioned further down) exists in Rhino 5. The rule of thumb I use to imagine what surfaces are developable is to think of a surface being created by straight ‘stick’ that travels on top of two curves. The surface created can bend only in the direction of the stick’s travel, but not along the stick itself.
My understanding that Loft tool does not necessarily have to create developable surface and it does not work on the curves that cross. DevLoft should create developable surface. For it to work though it’ is best to make sure that the curves are quite smooth with not too many control points as I had experienced it giving unexpected results if the curves were not very ‘clean’. Help menu of each of these commands includes a fair share of information as well on developable surfaces.
I fully agree with bjorf’s point as well, that every model is only an approximation of reality. The question of tool selection in the model will depend on the accuracy needed and tolerances required to produce a ‘good enough’ model.