FYI, the easier thing to do is to call the Plat desk after the promo ends and ask if there is a better Megabonus promo for your stays during the promotion period. They will be more than happy to check for you.
In my case last Megabonus promotion I didn't even have to ask. I called about 3 weeks after the promotion ended to inquire about stay credits for the current promotion. I casually mentioned that I had a 14 day stay from Jan 17-13 which didn't qualify for either promotion since it was in the dead zone between promos. I also indicated that I didn't earn anything in the previous Megabonus promo period. The CSR said wait one minute... she came back and said that I qualified for 5000 points under the 2 or 3 stays Megabonus promo so she credited my account 5000 points for the previous Megabonus promo.