13. For the back body part, I've simply done this the same as I made the other parts, but I was very careful not to add too many edges and make the form complicated before I got the basic form. Again, I simply extruded edges (shown in the next image), made them follow the blueprints' outline, then extruded again whilst following the blueprints to get the exact curvature (Fig18 and Fig19).
14. Then I simply extruded, or "copied”, the edges of the wheel arch to get this (Fig20 and Fig21).
15. This is a quick drawing of a wireframe over the back of the car image reference. As you can see, it's nothing fancy, but it helps us plan what to do. You don't have to do a drawing yourself, but if you can visualise what edge loops are needed before you do them, it will be enough (Fig22).
16. I copied the edges to get the main space, then made a cut along the edge I had in mind, and moved the vertices to get the correct form (Fig23, Fig24 and Fig25).