Rutherford Platt is correct. If you know the intrinsic clo for one garment, of a specified size, in a similar manufacture's series, you can estimate the clo value for all of the garments, of a specified size, in that series. For example, if you know the intrinsic clo of a MB UL jacket, you can approximate the clo value for the MB UL vest, jacket, and parka. They all cover a different % of your body surface area (BSA). The clo value will increase as the BSA covered increases.
The amount of down is increased about 7% for each size increase for down garments but the synthetic areal density stays the same for synthetic garments. So there is a slight calculation difference between down and synthetic mixes.
The simple thing to understand is that a parka will have a clo value about 7% more than a jacket. A vest will have a clo value about 25% less than a jacket. A down jacket in size large will have an intrinsic clo value about the same as a size medium jacket and a clo value approximately the same. A synthetic jacket in size large will have an intrinsic clo the same as a size medium jacket and a clo value which is slightly less.