Most manufactures change the names if they make an upgrade of some sort but very little really changes. Many will make the upgrade available on older models once the newer models have been on the market for a while. Some manufactures will use the same parts in many of their regs but they will have different part numbers for each different model. There is no correlation between 1st and 2nd stages within the same manufacture or other manufactures for that matter. Did you have a specific question about two regs?