I need to travel DAY-PVG ~3rd-4th weeks in October and am somewhat flexible (8 possible outbound and 4 possible return days). The typical availability of BC seats ranged from about 10-20 (777 DTW-PVG) and more for the 747 (DTW-NRT-PVG). My strategy has always been to purchase a M-fare and upgrade, but only if it can be confirmed at purchase, and usually I am able to do this at least 2 months out. At present, only 1 day (outbound only) is M-fare upgradable ($3,300), and that is via the extra connection through NRT.

My questions:
(1) Does anyone have experience purchasing such a fare above (only 1 leg confirmed and about 3-4 weeks out) and having the other leg confirmed before the date of travel - or will DL wait given the number of seats left?
(2) As I would be confirmed on the DAY-DTW-NRT-PVG routing, would the gate agent have the discretion to switch me (on the day of travel) to the DAY-DTW-PVG if BC seats were available?
(3) Anecdotally, I've heard that upgrades originating from China are not available on the day of travel due to planning considerations. So I guess if the upgrade confirmation for the return didn't occur in advance, I'm in the back. True?

Any other suggestions appreciated!

Many thanks.