Thanks to everybody for all the lively discussion.

In the end a number of pax must have misconnected because we went out with at least a dozen empty seats. I managed to grab a C+ window at the gate and I saw one pax get pulled out of C+ into J, I assume as the gate agent cleared his GUC (there were several names on the upgrade list) when the original occupier of the J seat misconnected.

I would still prefer that the app would show the "oversold status" of the flight, that is seats - confirmed pax. This is the most useful date point to me when trying to bump and what agents will quote you when you volunteer.