Great Question! I personally love this brand and have read about this, this is a tricky subject because each color uses different pigment particles. The best answer I can give is that light-fast within pastels matters a bit but it is more important how the artwork is displayed. So if this artwork that has these pastels is displayed with no UV protection coating on it as in a fixative or behind a UV protection glass/acrylic, then it will surely get destroyed by the sun.
Now if you want archival artwork, the pastel doesn't matter as much as using an acid free paper/board and using a UV protection fixative on top of this pastel artwork, then storing in a frame that has a UV protection Acrylic/Glass on the outside. This is the only thing that necessarily matters to your artwork more so than the light-fastness of the Reds and Blues from this brand. If you can protect your artwork and paper from UV light then there shouldn't be an issue. Pastels are sensitive to the touch and light in general and should always be properly protected from the elements to help with conservation, this might be why there isn't much information on light-fastness of pastels because most people seal them and prevent direct sun exposure as a measure of good practice.