I was supposed to be on a reconfigured 757 last night DL 1676 ATL - MCO. I get to airport and I was third on upgrade list with two possibilities. I then notice that total adds to 24 not 26. Sure enough, a regular 757 had been substituted. I asked gate agent if there had been an equipment change; she said no. Then they started boarding. Many seat dupes. One person had his seat downgraded at gate. They had to get a couple of non-revs to leave the plane after they were seated. I ended up in the back of the plane missing upgrade by one. First time I had ever seen gate agents confused by an equipment change. With four different (0 first, 22 first, 24 first, and 26 first) 757 configurations, and only two different designations (757 or 752), I wonder if this problem will continue for a while.

Marc