It is a zero sum game as although a commencement notice has not been sent it is an authorised development with the exception of the breach of one planning condition. If the commencement notice is sent in retrospect then the breach would be deemed to be rectified.
The one provisio on this is that the structures built complies with the plans and particulars i.e. the scale of buildings, location and materials as approved in the planning grant. If not then it is a question of whether there is a significant difference between what has been granted permission and what was actually built. If there is/are major difference(s) then it would be a case of part of the development being unauthoised.