Please see below the text from their website explaining the upgrade benefit. Maybe they claim the suite in question is 'one-of-a-kind'...the other 7 similar suites have a different room number
On a more serious note, if you're asking the get the upgrade confirmed before check-in, they have the right to ask you to pay for it IMO. If at check-in the suite is available and they are asking you to pay, then you could produce a print-out of the below policy and argue.
