@spikeyxxx I’m thinking at the edge of the fuel tank cap in the first of your three instruction images where diagonal edges are visible in the upper left and lower right corner of the cap outline. These edges are obviously not part of the original rectangular grid cell mesh. In this case, the cut-in edge loop has a comparatively simple structure, but what if there is a more complex pattern with a lot more of direction changes and details?

This has been cut in only with “Knife Project”. Now I use “Triangulate Faces” and then “Tris to Quads”, but this dosen’t guarantee you a good result, as the edge beveling shows:

The original file with the cut-in edge can be found here.