While not a comp for material the Louisiana Superdome has a white roof that needs needs frequent pressure washing because of mold growth. In that case, a company did some work to "guarantee" against fast mold growth because it was costing +$100,000 each time to pressure wash and it was happening about every two years but was probably needed at least once per year. That ended up in a lawsuit and I'm unsure where that went but it does seem like it gets cleaned every year now right before football season. Also comparable because it's literally the Superdome's roof and gets sun all day but still gets moldy.
That's all to say that contractors will say what they can get a job and then it doesn't always work out as promised.
That's all to say that contractors will say what they can get a job and then it doesn't always work out as promised.