I found a great chart created for a sewing blog that I want to share with you. You can review the chart here. I want you to notice that there are 6 different pattern companies included. The sizes run from 4-26 American and 30-52 European. Only one company gives a chest measurement. Look for the variation between the companies, measurements can differ by as much as 2.5 inches. Look for the petite measurements. There aren't very many are there? In Canada the average woman falls into the petite height range. Check out how many companies list shoulder length. Look at how the grading is done, does it appear to be consistent within each company to you?
The point I'm making here is that these differences all reflect standard measurements. The standards are specific to specific sources, they are not standards that apply to all bodies. This is why it is so important to compare your measurements to those of any pattern (sewing or knitting) and to make the necessary adjustments for good fit.