These oxidation spots appear to be fairly small, and they are only superficial, so they may be considered cosmetic. These oxidation spots would not likely affect the functionality and solderability of the resistors, considering the large area of the lead wires for mounting the resistors on the PC Board.
It is still not possible to make a conclusive statement on whether the oxidation shown on the images will affect the function of the parts or the solderability. For more specific analysis of the situation, samples of the pieces exhibiting oxidation will be needed for failure analysis at the factory.
Applicable Part Number