Vinyl flooring discolouring

Simel

White vinyl contract flooring was fitted in three rooms, toilet and utility area last November. We were told it was hard wearing. Self levelling compound was needed in our kitchen and another large room - small ridge in large room and can feel something uneven in kitchen since having this done.Vinyl has discoloured yellow under mats by back door and under rug in large room, but also under wooden furniture that only touches floor at the feet and anywhere light does not get to.

Complained to retailer, and independent inspection report concluded problem is caused by plasticizer migration/antioxidant staining. A combination of atmospheric contaminants, moisture, light and other conditions come together for this problem to occur. The effect is gases rise up and cause a yellowing discolouration. Certain compounds added to rubber (mat) can discolour a vinyl floor when in contact with it. But yellowing is also under furniture.
Report referred to yellowing being known as antioxidant staining in the vinyl industry.

Manufacturer says there is no manufacturing defect. We were not informed by retailer that mats and rugs could discolour vinyl in this way.Retailer is offering 50% discount on new flooring and fitting. Having had vinyl fitted we don't want more fitted if the same problem occurs.
What is reasonable in these circumstances?