The letter at the end of HP inkjet cartridge numbers signifies the volume. Most HP cartridges only have one type such as the #56 which you will also see shown as the C6656, C6656A and C6656AN. HP sometimes shows the cartridge as the 56A or C6656A, but the full part number is C6656AN. All version are the same product with the same ink volume. Only if the first letter after the numbers was different would it be the same cartridge with a different volume. Other first letters at the end such as 51645G and 51645A are the identical cartridge, but with different volumes. The G is the free starter cartridge that comes with a printer and the A is the regular high volume cartridge that is sold in stores. When our cartridges are manufactured we always fill the cartridges completely. So, regardless of the letter at the end of part number or the letter you are used to order you will always get a high volume cartridge for us.
Some cartridges come in big sets for example, 4 black and 2 of each color. Can the cartridges be mixed around within the set so that we can get more of one color than others? No. The cartridge sets can not be mixed. We have price breaks on the individual colors so you can order them individually to get better prices on them.