I know he is meant to come back at the end of Reborn, but Steve was already back as Cap in the latest issue of Iron Man, and before that in Dark Avengers annual 1. Have I missed something or is it all due to delays and books coming out in the wrong order?
It's definitely more of the latter than you missing something. Reborn was supposed to be five issues, they've padded it to be six. This means it will truly "end" in January when Seige is already going and all books show Steve's back.
Iron Man, the DA Annual, the NA Annual... all these were to coincide with Reborn being over this month and the "secret" out, but looks like Marvel couldn't keep to a time schedule, lol.