Inner Fender Difference

[mechanicmangg]

81 Malibu and looking to order front inner fenders.
Notice that the Monte Carlo inner fenders are less in price and in-stock everywhere.
For the Malibu they cost more and out of stock.
They have different part numbers but look identical.

Does anyone know what is the difference between them?
I know you have to drill the holes for mounting, don't understand what could be that different.

Thanks!