Proper Method for installing tar paper on side of mobile home

[David Banner]

I just had a contractor put up new exterior wall panels on my 1973 mobilehome. But first he added rows of tar paper going from left to right horizontally. He then added a top layer at the very left ( about 6 inches wide )that runs from top to bottom "over all" the horizontal pieces. My question is: should he have laid that left vertical piece in "first" to keep it behind all the horizontal pieces or should it be on top as he did it, or is it also possible that either way is just fine? I want to get an outside opinion on this before I ask him about this directly, in case I am just being too anal minded about it.