"Also, it is possible that modern complex systems have evolved considerably
since their assembly, concealing the evolutionary pathway. I'm not sure how
one could test to differentiate between design and lengthy evolution.
The point that Behe makes is that so far nobody has succeeded in identifying
or studied the evolutionary pathway whereby complex systems evolved. In
fact, his search of the literature shows that no one in the molecular
evolution field has even tried. I suspect that "lenghty evolution" may not
be involved, but rather a gestalt-like process whereby all the elements are
assembled simultaneously. The key event may be the presence in a limited
manifold of all the essential elements that are needed to make up the system.
Lengthy evolution may then add details.