Answered: NEC3 ECC: If the Employer reduces the scope of the works to be completed, does this automatically adjust the Completion Date?

No.

This will be a compensation event, which will lower the total of the Prices, and also bring forward planned Completion - but Completion Date does not move. The only real benefit to the Contractor is that they wont be charged Delay Damages until after the original Completion Date.

The only way to bring forward Completion Date is through "acceleration" under clause 36.