Designation of W-Sections

The designations of a W-Section is chosen such that the first number represents its approximate depth and the second number represents its unit weight.

My question is: why there are many deviations from this rule?
For example, W36x652 section has a depth of 41.1". So, why wasn’t it grouped with the W40 family? Note that the depth of the sections in the W40 family ranges from 38.2" to 43.0".


The nominal depth class is based more on the flange to flange distance measured from inside to inside, rather than outside to outside.

Above is a snippet.