First Ever SDC
 

I contacted the Platinum line only to see if I could get an agent to tell me if I had half a chance to do a SDS for an earlier flight tomorrow. Didn't know if they could/would tell me there were seats available, but if they could and there were no seats, I didn't want to check out of my hotel at the crack of dawn and end of sitting at the airport for 5 hours because I wasn't successful.

I was told that if I wanted, they would confirm seats on the earlier flight I wanted. I booked an X fare and the flights I wanted were a U fare. Pleasantly surprised at how easy this was given the fact that I thought the fare I purchased had to be available to do a SDC!

There is often open fares for classes that aren't for sale. Last month I had a LGA-DTW-OMA that was only selling K fares online but had open availability in all fare classes for SDC. Expertflyer and Flight Stats(free) have this availitbility

Probably more often than not.

I SDC'd last week and the agent said there was availability in U, which is what I had booked, but the BP showed L and my DL.dumb readout shows L/L in the paid/flown section. So I think I had a very friendly agent who cut a corner for me.

I've only had to SDC four or five times this year and haven't been forced to SDS yet. YMMV.