Please note that you can decide on the interface you want to implement.
Does it mean we have to choose between one of National Administrator / Regional Administrator / Exibition Organizer interfaces?
Or should we just do everyhting in anycase?
Then what I suggest is that you state at the top of your assignments that the requirements were a bit vague and that you chose to interpret them the way you did.
I also understood this to be a case of "choose which interface to build", I.e.: Regional Admin, etc.
It also made sense to me for the sheer amount of work (especially when this isn't your only subject). By doing the other interfaces you'd also be recreating things time and time again. I did state which interface I chose to develop, so I suppose time will tell.