The T&Cs called for upgrades based upon availability at check in. This was long before OLCI was an option. Given many of the properties where I have stayed pre block their upgrades (and reflected online before arrival) that was pretty much out the window. And with SPG sending a preference list, that also shot down availability. Now there have been instances where I asked about an upgrade at check in and I was assigned a different room only to find a welcome letter/gift addressed to the previously assigned guest. I'm just waiting for them to send us all up to the bar/lounge until 6pm and then dole out the upgraded rooms at that time. Of course you'd be free to accept what's available upon arrival, if you need/want to settle in early.