Is the number of physical pieces also the limitation of the maximum number of allowed pieces? Specific case: Germany has 12 tanks out of the box, and 9 on the board of starting set-up. Can Germany ever have more than 12 tanks at one time?

Is the number of physical pieces also the limitation of the maximum number of allowed pieces? Specific case: Germany has 12 tanks out of the box, and 9 on the board of starting set-up. Can Germany ever have more than 12 tanks at one time?