I wanted to move 2 free night certificates from a reservation at a category 4 hotel to a different stay at a category 5 hotel a few months ago. So to avoid calling customer service, I cancelled the first reservation with the 2 certificates, and then waited for the certificates to come back to my account. This usually happens immediately, but an hour later, they weren't there. I must have gotten lucky, because when I called the platinum line, I got an agent that knew exactly what had happened.

I was told that after one of the December updates, the way certificates are handled within Marriott has changed. Specifically, the certificate is sent to the hotel immediately upon booking now. So when a reservation is cancelled that uses cc free night certificates, the hotel has to manually release the certificates in order for them to go back into my account.

The agent called the hotel for me. Luckily, it was still normal business hours for the hotel in question. After about 10 or 15 minutes on hold, she said that the certificates had been released by the hotel, and they should be visible on my online account. So while she was still on the phone, I logged out of my account, and then logged back in. Sure enough, the two certificates were there (1 - cc cert and 1 - PP 40K cert).

While she was still on the phone, I booked the two nights for the category 5 hotel I wanted to use the certs for online. It all worked out.

I know that we hear different stories from different agents. But from what she told me, the safest way to cancel reservations with certificates attached is to call the hotel or customer service so that the certificate can be manually released and put back into the account.