Looking good!
Umm..I was going to say ours had self stick web tape where seams were and thats what I used before sanding edges. But looking back thru your pictures what I am seeing is there is no support at the seam? I assume the forward vent Not the one in pic is the AC hole? The hole close to seam is standard vent.
I can not see how the seam, as both in/outer panels and foam are cut, will support itself. At the vent hole 1 1/2"-2" of panle that last 14" of forward roof will try to flex at the back of hole. Or the only support and what will try to stop flex is the vent itself? It appears the seam was further back before over wall but now the span is from outside wall?
Im not sure, maybe get creative add an internal support from cabinet wall to mid wall under seam, but might whack your head. I just cant see how that seam isnt going to move & flex, let alone hold any weight?.
As to the tape I dont think will stick, though if captured and full sheet of rubber on top would probably stay. But you could add another layer of laun to resurface entire roof (as mfg. recommended), then you could overlap the seam. Unless Im way off and seeing this incorrectly.
If 4' would take you past the vent, not wanting to resurface all of roof to cap/nose joint, thats what I would do at minimum. You could feather sand the edge. Or start a foot forward of vent, even if you had to add at rear of roof. Be better than having open floating seam in roof. Even so Id put some cribbing inside to support my weight.