OK DM here. I thought i had figured out the "manage upgrade" thing for immediate access to C+. Booked a flight today. Went to the web site, clicked on the manage upgrade thingy, applied to to all segments, and then went back in and was able to select C+ seats as planned.

HOWEVER: i then got the "upgrade confirmed" email about an hour later, went back in and all of my C+ seat selections were gone, i was back in regular economy and I had to do it all again.

Glitch? User error??(wouldn't be the first time for me!!)