Mulch being an organic product will bio-degrade in time. If the much is too deep a chemical reation will allow it too heat up, create moisture and mold. The same thing can happen in hot
weather while it sits in an enclosed bag.
Therefore in your yard do not let the mulch get too deep, and at least once a year turn it over
or fluff it. This will ensure that air is getting through it and will keep it from molding. Check around your plants and trees for signs of mold. Pull the mulch away from any suspect plants to create an air flow.
Glad to hear the company stood behind their product. This is just an FYI on mulch.
Good luck selling your home
Judy - Ludington Landscapes - Longmont