Deborah, I don't think your explanation is correct. That law only applies to fabrics used as pajamas for children. It does not apply to batting or other cottons.
The law refers to the bit of poly stuff which is the scrim mesh. The total product is partially poly, due to this scrim, so they have to include the 87%, 13% or whatever it is to comply with the law. The actual batting is 100% cotton.