In your original post, that issue looks exactly like a mirroring issue. The UV's weren't mirrored or the mesh itself was not mirrored properly and didn't accept the mirrored UV's on one side. It doesn't look like a normals issue, but I haven't worked with 2.79 in years, so I don't really remember if that's something I've seen before with the normals.

The black spot looks like artifacts I've seen happen with baked textures where vertices somehow get out of alignment with the UVs during lighting calculations. I'm going to assume you didn't do any baking on this project, so that's probably not what happened there.

I definitely would start this model over again, because there's a number of issues there which may or may not be "fixable" at this point. Luckily it's a very simple mesh so it shouldn't take much time to start from scratch. If it's not too much trouble and you wouldn't mind sharing the .blend file of that problem mesh, I'd love to have a look at it. Especially the black spot is something I've only seen before with baking issues, so I'd really be interested to know exactly what could be causing that. If you can't share the file I understand. Good luck on the new model.

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