Some expensive fabrics still can run! I can tell by the color of the water when I have pre-soaked a piece in a pan of warm water. My Thursday group quilt instructor always pre-washes her fabric and on a piece she had done a few yrs ago that was a UFO she accidentally spritzed part of it with water. In this piece she had made glasses out of red fabric. One side of the glasses bled (giving her face a look like "pink eye" and the other side did not! Now she has to find some fabric paint to fix the glasses as all they remedies she tried to remove the bleeding failed!
If you cut a small piece and pace it in a measuring cup with hot water and it bleeds, then I would soak the fabric in retayne and wash with synthrapol.
Have had red, black, brown, purple, blue and green run on my pre- tests.
If for a quilt to be used and washed then at least test to see if any of it runs. If for a wall hanging you could skip this step
just my experiences with fabric!