Reading this thread makes me think about other threads on breed standard.
Seems to me there is standard and there is reality...and the reality is that Shelties continue to come in all shapes and sizes, despite careful breeding. I suspect the Sheltie line is still too new to get consistency. Let's face it, the breed has been around for less than 100 years. It's not surprising to find even in one litter one going over and one going under standard.
And we can't forget that the difference between European and North American Shelties. European tend to finer bones and smaller compact bodies. NA dogs tend to be more bone dense and longer and leaner, in my view.