My week of meetings looked like it might be ending a day early and I thought about the possibility of doing an SDC to change from an afternoon flight to a morning flight today (Friday). My original flight was at 3:00 p.m. and I was booked in V. On Wednesday evening KVS (Sabre) showed V0 on the flight I wanted (9:44 MCO-DEN) but the higher economy classes were 9. As I understand the process (and an agent confirmed this) I couldn't do the SDC at the 24 hour mark because my booking class was not available. The agent said that seats are usually released to all classes about four hours prior to departure (meaning 6 a.m. Friday morning). I checked again via KVS on Thursday night and the 9:44 flight showed F1 and zeros in economy via Sabre. So I figured it was impossible and gave up. This morning I woke up around 7 and when I looked again Galileo showed V3 on my flight (Sabre doesn't show flights that are four hours or less till departure).

So here is my question: Is it normal for a flight that is zeroed out in economy 24 hours prior to departure to go back to showing space available the morning of the flight? I don't fly CO/UA very often (most of my flying is in Europe) and I figured once a flight is gone it's gone. If I had known that things were this up and down, I would have packed Thursday night and been ready to try again first thing in the morning instead of giving up. I will face this again in the fall, so I would appreciate any insight in the process.