Another upgrade data point: I ust booked a 3 for 2 IHG Destined rate for a Cosy room next weekend. When contacting the hotel asking for which upgrade to be expected I got this reply.
First of all, thank you for being an IHG Diamond Ambassador with us, we truly appreciate your continued loyalty. As part of your exclusive Ambassador membership, you are entitled to a guaranteed one-level room upgrade. In addition, as your reservation was made through IHG Destined, you are also eligible for a further one-level upgrade, subject to availability upon arrival.
As you last stayed with us some many years ago, I am very pleased to confirm that we have arranged an exceptional three-level upgrade for you to a King Premium Park View Room on the 7th floor, overlooking beautiful Hyde Park.
Quite generous. Haven't been to London for over 2 years and very much looking forward assuming nothing comes up in the meantime.