The Guest Rewards Redemption Page shows..
Space-Available Upgrades
5 One Class Upgrades4 10,000
6 One Class Upgrades4 10,000
They're the same points, any reason why one would choose (5) of them versus (6) of them?
The only caveat on them is
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">One-class upgrades valid day of departure only, based on availability one hour prior to departure time. Coupon cannot be used for sleeper accommodations. Other restrictions may apply.</font>
(I assumed that the caveat might explain the difference but it doesn't seem to. Am I missing something?)