The gate agent for a YYZ-YVR A321 flight said the same thing last night. My friend was top of the waitlist for a J seat but the flight did show them all being full. With no PY she waited at the gate hoping. I texted her that 4 seats were still empty after those who boarded with zone 1 and 2 had loaded and she waited for awhile longer but finally thought there would be no overhead space if she waited any more. As soon as she boarded her name disappeared from the waitlist.

All four J seats did fill but who knows if anyone who hung out at the gate longer grabbed on of them.