It seems like if you need to "shingle" the layers of tape, than the Zip tape is vulnerable to leakage or not adhering properly. In thay case there there is potential for leakage throughout. Overlapping zip tape shouldn't matter if zip is doing its job. If you shingle above windows, do you at all places where vertical and horizontal pieces meet on walls and roofs? That gets very difficult to install correctly when doing a whole house.
