My answer is based on what I remember from posts by forum members who recently got their distance certificate.
As you will see, or have seen already, in your case you have these three options for selection (in English): 1. Camino de Invierno, 2. French Way, or 3. Otros Caminos [=Other Caminos]. The chosen Camino determines the list of starting points from which you must select one - in case 3, the list is very limited, and the same applies for case 1. If you select "French Way" you have the option of selecting Lourdes as your starting point. These choices are of no importance for qualifying for a Compostela as you know.
When you wish to receive a distance certificate, you need to tick option "Print mileage certificate".
With this long description out of the way, here's the main point: Before the distance certificate gets printed at the Pilgrim Office, you can discuss the details with the member of staff or volunteer in question, and they can modify the data appropriately so that several Caminos and the correct starting point will be recorded on your distance certificate.
As I said: This is based on how I remember comments by forum members who 'have been there and done that' very recently.