I don't know the defined standard for select and better grade. But I have attached some photos of the treads I received. The photo of the one with the knot is the most variable board regarding appearance, all others look even more uniform. The photo of the end grain is to demonstrate that the boards are not quarter sawn, which may be the industries term for the most select boards, I've never seen an quarter sawn boards for flooring, I think you would only find it now days in furniture use, because of the expense of quarter sawing. You can also see by the end grain that the treads are edge glued boards (each approx 2.25 inches wide) which is really better because treads glued of separate boards will have no tendency to warp or twist, and these boards are perfectly flat with no bow, no cupp and no twist. I have ordered 11 on two different shipments, and I am completely happy with the product.
Here are the photos, note that any curved appearance of the boards is due to photographic distortion from the wide angle camera lens.