Important: one should understand that a finished product is stretched on the stretching frame first and only then the measurements are taken. Therefore, the true dimensions (in centimeters) of a newly made down shawl are correctly determined only when this shawl is stretched. That said, a brand new shawl tends to "behave" as a "living being." When removed from the stretching frame, the item would "shrink", and the distance between the rows of loops would reduce; therefore, when measuring a shawl removed from the frame, the length of each side can be much smaller than expected (and not correspond to the true dimensions).
The same principle works for packing and transportation of downy products. In fact, a downy shawl that has just been taken out of a package cannot be measured, since its dimensions in centimeters will not be correct ones.
Of course, there is little chance that you have a stretching frame at home. Besides, this "forced" stretching is not the only way to measure the true size of a downy product. There exists a much more natural way:
First, take your downy product out of the package and thoroughly straighten it (it is important to remember that the loops got "shrunk" a little in the process of packaging and transportation). Then the fully straightened product can be left outside, to hang on a line in windy or snowy weather. After some time, your shawl can be measured, and you will see its true dimensions (with a possible error of no more than 10 cm).
The same applies to the process of wearing a downy shawl. One can say that a downy product "breaks in" over time - similar to new shoes (in a way). The process, as you already know, does not take much time. In other words, after a short time of use the product will get slightly larger than before, but the down shawl won't look "shrunk", as the "increase" is due to the downy fluff "standing up" in the process of use.
So, the "true" size of a down shawl in centimeters is determined either by stretching the product on a stretching frame, or by following the above-described procedures (when the straightened shawl is left outside on a line in cold, snowy or windy weather); the shawl also could be measured in a fully straightened state after a certain time of use.