Ok, that seems to have worked. So the Rennbow site lists two color codes for Pewter Metallic; 655 and 956.
A Google search of ‘Porsche paint code 655’ results with lots of Platinum Metallic hits, and sure enough even the Rennbow site lists 655 as one of the listed paint codes for Platinum Metallic. Trouble is, the sample images of cars shown on the site for Pewter Metallic and Platinum Metallic are quite different from each other, so why would each of these apparently different colors include a reference to paint code 655?
A Google search of 956 brings up Zinnmetallic which translates to Tin (zinc) Metallic, and Pewter Metallic. The more looking I do the more I see these names appear to be somewhat interchangeable. Rennbow describes this way: “Tin is a slightly smokey shade of silver with a hint of platinum in it. And oh, does it look nice with a red interior. As an aside, in English, the color is sometimes referred to as Zinc, however, the German name for the color, "zinn" translates to "tin" in English.”
The Ellferclassic site also lists 956 as Zinn/Tin metallic (pewter not mentioned).
@bee4bee have you tried paint code 956 for possible touch ups? I would be curious if this is close to what you have, although screen images of photos of cars portraying Zinn/Tin Metallic appear a bit lighter in tone than your images.