It depends as it could be a couple different scenarios.

As you mentioned, it's possible that there could be held seats for weight restrictions that get released at the last minute. You'd probably want to mention the city pair and dates so a 747 driver can chime in.

But also----IF economy is permitted to be oversold the system will automagically hold seats in F or BF. Premium pax will get upgraded into the held seats to make room for the economy folks so you will need to look at total bookings in all 3 cabins to get a feel for the actual load. FWIW, you will also occasionally see this domestically.