Ok, this is interesting. If I try to add an additional bag, the app and website allow me to add it for EUR 0. So in the back-end at least, the 2 additional bags is recognized. But once I complete the process, the bag doesn't actually appear as being added to the allowance.

I guess this means that at least we won't encounter the need to pay for an additional bag while checking in, since the system seems to recognize the +2 additional allowance somewhere.