I booked 6 nights at a Cat 4 online and it deducted 60,000 points. I needed to change the res to 5 nights after the fact, so called the Plat Concierge, who pointed out the "stay 5 nights for the price of 4" thing they have, and after correcting the res, it added 20,000 points back to my account. I was surprised that with the "5 for 4" when you book 6 nights, it doesn't take that into account and only charge you for 5.

Another reason to love my concierge!