Do you have to place all your nobles during the wintering phase or can you keep some of them in your undeclared pool? I know all officers have to be placed, but what about non office holders?
From the rules (27.2):
A Player having no unplaced non-Officer Heirs may pass instead
of placing a Noble; if they do so, the remaining non-Officer
Nobles controlled by that Player become Undeclared (8.2) and
are moved to that Player’s Undeclared Pool.
Note that as soon as you pass, all remaining non-officer nobles go to the undeclared box. It's a good idea rather than having an isolated noble. Plus, you might have a card that lets you place undeclared nobles during the action phase.