Originally Posted by
Naggi
I understand more seats may be sold
Yep.
Originally Posted by
Naggi
or Y/Y+ passengers upgraded etc...
Nope.
Even with the mini-cabin "full," it will not matter much to your experience. And the second cabin is quite likely to fill up before day of departure, except on very rare occasions.
Stick with the seat you have reserved, unless you really want a bulkhead.