I just renewed my AP for the first time too, and it came on a green card that had to be activated and it said to bring the letter also. The AP dates remained the same, so for check in at your resort you technically have an AP although the card mailed to you won't get you into the park until you exchange it at any customer relations desk. Renewel APs begin at the expiration date of the other, not when you first use it. The CM at AK said the card was just like cash, which he then exchanged for the actual AP.