My aunt has a Duoclear 35 system & has been changing her mineral cartridges as they say to. She has been getting them online with no problem. But the latest one she got looks different at the top. All the previous ones have been a yellow top that sort of looks like a hat. This latest one has a top that's gray & has no domed top. It has 4 prongs along the edge but is not like the electrode where the prongs are inside the top. The new cartridge looks identical to the old one except for the top. There is a code on the bottom of the thing W17020REV8 or B (can't tell about that last digit). Has anyone any idea what she got- is it a new design or a defective made one.