Key Dates is a defined term at clause 11.2(9) which the Contractor has an obligation to meet at clause 30.3, the Key Dates are found in Contract Data part one. The programme requirements at clause 31.2 require the Contractor to show the Key Dates and also when he is planning to meet the Key Dates. The only mechanism for changing a Key Date is by compensation event, if the Contractor can demonstrate that the event will delay when he was planning to meet a Key Date (clause 62.2 and 63.3).
Therefore the PM has no right to instruct changes to Key Dates per se, however a PM’s instruction may impact on a Key Date, for example additional works i.e. a change to Works Information clause 60.1(1) may delay the Contractor from meeting a Key Date.
So what the contractual status of “Milestone Dates” (which is not an NEC term) stated in the Works Information is and your liability to achieve them will be down to what it says in the Works Information. Technically a “Milestone Date” (whatever that is as the NEC doesn’t tell me) is not a Key Date therefore the provisions I’ve mentioned above do not apply to them. There may however be other obligations imposed on you in the Works Information. If not then the PM has no right to instruct changes to Key Dates and that instruction does not have to be complied with as it isn’t in accordance with the contract (clause 27.3).