Sorry to disappoint you, but your TA gave you very wrong information. Here are the guidelines for dress in the current version of Princess's Cruise Answerbook:
[i] Dressing Up
When you're in port, evening dress is casual; slacks, sweaters, blouses, open-neck shirts, etc. are typically worn. Shorts, cut-off T-shirts, "torn" jeans, and bare feet are notpermitted in the dining room.
For semiformal evenings, passengers dress as they would for a fine restaurant at home, with ladies in skirts/dresses/pantsuits and gentlemen wearing a sportcoat or a suit.
On formal nights, ladies perfer evening gowns or cocktail dresses and men turn out in tuxedos, dinner jackets, or dark suits. [i]
You have to return the forms in the information package with your measurements and selection of formalwear to arrange rental of formalwear through Princess. If you choose this option, Princess will deliver the formalwear to your cabin on embarkation day and you simply leave it there when you vacate your cabin at the end of the cruise.