@Ivo
You said the steering wheel buttons Vol+ and Vol- are swapped. What about the other buttons (Call/Speak, Hangup/Mute, Src+, Src-, Src (push)) ?
There shouldn't be many further buttons in the Corsa E. Lighting, seat heating and maybe climate controls (if you don't have the simple/manual A/C).
What about door opening detection, parking distance detection and warning signals (key, light, etc.).
Do they all work as expected ?