It seems that photographers (especially those of us that like to think of ourselves as "fine art" photographers) seem to think that if anyone else but us touch our precious prints that they will not be "ours." Hogwash. Working with others requires that some adjustment be made to allow the project to supersede the personal vision.
More examples of the collaborative? Strand's "Time in New England", any book of Atget's photographs and Morri Camhi's "Prison Experience."

Heck, for that matter any book of photographs is a "team" project.