OES stands for Original Equipment Supplier, which means the parts are made by the same company that makes the vehicle. Meanwhile, aftermarket parts are produced by a different parts company and are often designed to be compatible with as many makes and/or models as possible.
Part #'s
3B1-837-015-AT / 3B1837015 AT / 3B1 837 015 AT / 3B1837015AT
3B1-837-015-P / 3B1837015 P / 3B1 837 015 P / 3B1837015P