Principato: availability of cubes
There is no FAQ from the designer, and he has never answered definitively on BGG, but without any rule in the rulebook to the contrary.

The cubes are lmited.

For example, take:


Monopoly the houses are limited, but cash has a specific rule that it isn't.
Puerto Rico the goods and buildings have a limit, but if victory points run out keep track on paper.
Race for the Galaxy the VP points if you run out, you are told specifically to keep track some other way.


Unless a rule tells you otherwise, I would assume that components are limited by their physical natuire unless otherwise noted.