I’ll be very careful in saying this… but you can also pull the seat map using cowtool’s Flight Status tool.

Of course this isn’t an exact science and plenty will say “Stop looking at the seat map”

However, I have found it a good general indication of how sold the J cabin is, despite its limitations (there can be sold seats where the passenger hasn’t selected their seat, seat blocking, etc).

I do find it useful when I’m waitlisted for J on a J9 flight to better understand about how many seats might be unsold on top of the 9 that the fare bucket maxes out at.