Perhaps we can wait for AY to respond, but in the unlikely event where no one volunteers, I venture to guess that the ones without assigned seats would be the "IDB's".

I will also say that, based on experience, even if you do get a chance to board the plane you will have almost no chance to sit beside your travelling companion in such a situation.

That is unless, of course, you find a volunteer to swap seats.

All the more reason for OLCI!