Thank you Inspector. When you state "seams this large" I guess you really meant "seams this many", which then increases the probability of nailing shingles in close proximity to a seam or on the seam itself.
The same problem exists, if I understand you correctly, though less often of course, where the full 4'x8' sheets also incur a seam, especially since a 1/8" thermal expansion spacing is required. I guess the "H" clips then serve a dual purpose as spacer AND support.
As a "stubborn old coot", I could, with some measure of difficulty and ingenuity, glue or otherwise fasten plywood strips underneath the seams and solve the nailing problem, but at great expense to my standing as a "rational old coot".
I'll hire me some young bodies. Thanks again.