There are currently differences between Rebrickable and BrickLink for the spare parts:
54200 White - Bags 2, 5, and 6 have 1 spare each. BL shows only 2.
54200 Black - Bag 2 has a spare. BL shows none.
2780 Black - Bags 4, 5, and 6 have 1 spare each. BL shows only 2.
18979a 4 Flat Silver - BL includes these in regular inventory. They are shown in the picture, so to have a complete set, BL Sellers must include them. Because they are not actually used in building the model, Rebrickable considers them spares.