I have a feeling you might be correct in that assumption. That would explain the discrepency between the difference in "drops" between my "new line" reservation and my "upgrade" reservation for the exact same phone (6+ 6GB Space Grey).
Just checked status for 6+ 64GB SG. Went from #36 to IN PROGRESS. Reserved under new line system. Good luck everyone!
128GB 6+ Space Grey, 171, no movement for a couple days now.