i would wash it as the finished quilt would be washed. if the fabric won't hold up, i'd want to know before i went to the work of making the quilt

I agree with the others - wash it. Then, I would do a burn test to see if all of it is cotton or if some are poly/cotton blends.

I'm a prewasher anyhow but I'd certainly wash this as I'd want to know if there were going to be damage issues BEFORE I spend my time putting it into a quilt or any other project for that matter.