I went through similar frustrations when shopping for tires. I have found that it is much easier to look at the ISO/ETRTO numbers whenever possible (explained here by Sheldon Brown). So, once I figured out that 700c wheels have an ISO diameter of 622, and that the first number referred to width in mm, it became much easier to decipher the charts. For example, if you go by the "dimension" column on this chart, you will see that it jumps around between measurement standards, even within the same wheel size. About halfway down the chart, you can see the sizes progress like this:

700 x 32C
28 x 1 3/8 x 1 5/8
700 x 42C

Confusing. But if we just look at the ETRTO column to the left, it becomes much clearer:

32-622
37-622
42-622