I'm a little confused with the temperature or comfort ratings that go along with sleeping bags. I know it may sound silly as I'll likely be in a tent with tarps around it in hopes to brake the wind as much as possible, but do these ratings account for wind chill or feels like factors?

When I see 3 season bags which season should I assume is not included? I assume winter, but I usually don't encounter temps below +10 F in the areas I'm likely to be staying.