Additional data point, in case others have registered on Fast Track but not seeing any differences in status nights.
Looks like not all properties are part of Fast Track, but there doesn't seem to be a way to check this anywhere.
After verification, we inform you that the Novotel Metz Centre hotel is not participating in the "Fast Track – Accelerate your status" offer. Therefore, your stay at our establishment (reference: XXXX) unfortunately does not qualify you for additional status nights as part of this promotion.