Ok, so yours has the new PID controller which does not have the 275 setting. The one I have is the older controller which has Smoke, 150, 175, 200, 225, 250, 300, 350 and one or two more.
Really I have never gone by temps to cook anything. I just use internal probes. If you have something that says to cook at 275 try 250 and monitor with a thermometer. If you don't like how it is doing bump it up to 300. The good thing about the PID controllers is that they have less swings. If I set mine on 275 it will continuously bounce between 260-285.
My other Pit Boss is a grill and it does not have 275 so I just keep an eye on things. I have even baked a pie on it that was supposed to be at 425 and I do not have a 425 setting. You just kind of eyeball it to see how things look and having a thermometer is important.
Honestly I wouldn't worry about it too much. Some of the newer controllers have 10 degree increments (the 1500 I think) and there is no 275 since it adjusts by 10 degrees.