The difference between staining and mold on plywood

[Scott C Simpson]

This is the attic sheathing. Any thoughts on whether the dark spots are mold, or just stains?
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[Seamus Kelly]

I'd err on the side of caution and say that it's mold. You can get mold growth on plywood or OSB if the space is not properly ventilated. There may also be a leak from the roof, but i think condensation is more likely.

[Don Clendaniel]

Need to see more of the attic, but my call is mold. - NYS Mold Assessor