My point was that the reservation for the second night should be given to the desk clerk so s/he can combine the two and use the certificate to credit that night. If this is not done, then the res will show as a NoShow and s/he will be charged the full rate even if they were occupying another room. The front desk may not otherwise like the two bookings, even if you make the notation as I have suggested. Of course it will be up to the desk agent to process this accordingly. The point I was making is that one must ensure that the second night does not get billed as a NoShow.