When packaging the masks, sewists are instructed to include a packing sheet that includes information about the material that was used to make the mask.
Because any mask is better than no mask, we can't claim that any material is "correct." The only exception would be when a sewist wants to make the three-layer mask. If a sewist does not have the interfacing required, then although it is not following the material specifications of the mask, it is still a functional mask. This would be clearly conveyed to recipients of these materials.