the statement set out in Part II or III of the register of a drainage board differs from the statement which would have been set out if the initial date had fallen after that act or event, the board shall amend Part II or (as the case may be) Part III so that it sets out the last-mentioned statement;

the map of the drainage board shows particulars different from those it would have shown if the initial date had fallen after that act or event, the board shall amend the map so as to show thereon the particulars which it would have shown if the initial date had so fallen and shall delete any particulars which have become incorrect.