I have a slightly different experience. I have an email chain from before the transition from a Marriott supervisor that implied my OC8 would allow me to at least book a specific NC6 even after the transition.
Over the last month or so I have been trying to get someone to honor that and finally someone escalated it and opened a case and I was told I should have a resolution within 5 business days. 10 Business days later and not hearing anything I reached out again and then got a response there is no timeline on a response, which made me nervous as the cert was going to expire in a few weeks.
I then got an email from someone that was assigned the case and they said sorry its expiring you can get a refund. I reached back out and politely asked if he could cancel the original 950T certificate and apply the refund and an additional 30K it to a QP99 which my understanding would extend the current certificate. I was not expecting it to work... but got an email a couple days later reconfirming the new category 6 reservation and a follow up from the CSR confirming he took care of it. Was pleasantly surprised.