See, I also did the same. I work for a similar company.Booked through ACCOR website but with Microsoft corporate codes where I work
But there was a 20% discount offer from accor side on top of the chain rate. So that booking was not eligible for fast-track. I confirmed with accor. But I have few more bookings upcoming. If you have any upcoming bookings , just ask them if any of that are eligible for the Fastrack offer. They will tell.
I am staying 5 nights before December and one of them is eligible for the offer and I will get +5N.