Unsure on how CX grade bookings so idk if S is above V but we just booked our 1st CX flight and during the booking process it asked for FF details. I entered our BAEC details and it picked up on our OW Sapphire status and allowed us to book extra legroom seats for free during the booking process ( point of note: I dint have a CX/ Marco Polo account when booking. It didnt 1st time but booking crashed and when I tried again it picked up on status)

Flying BA 1st LHR-HKG then back from BKK in Business Class on an Amex 2-4-1 and had to do some arm twisting to get the lady to agree to CX as flights HKG-CNX are available a LOT cheaper but there was no way I was missing out on the CX lounges at HKG