First of all - Completion Date should not be a key date. They are different thing. Completion Date is the date the Employer requires the defined works in "Completion" to be achieved by. These would be liable to fixed delay damages that are identified in contract data part 1 at a cost of £X/day.
Key dates are a bit different. They are intended to be a requirement to achieve a certain requirement by a certain date e.g. to provide power to a specific part of the site by a specific date. This is normally to allow the Employer to manage Others (i.e. other 3rd Parties). if the Contractor misses this date for reasons that are their own fault, any resultant cost the Employer incurs as a result will be recoverable from the Contractor (25.3) i.e. undefined/unliquidated cost.
If there is no X7, then outside of the NEC contract the Employer is able to claim unliquidated cost, but if X7 is included it takes away this loophole. If you have X7 and delay damages at say £2000/day, then the fact they have made Completion Date a "key date" which is undefined cost in itself is an "ambiguity". This would actually go against the one who created the ambiguity (which here would be Employer). If the Employers overrun cost will be £25k/month then this should have been identified as the delay damage figure (say £1000/day).
Also worth noting that if the Employer puts delay damages at £2k/day, if they are losing more than that they cant claim any more from the Contractor. Same rule applies to sectional Completion Dates as well.
If there is a genuine key date that the Contractor misses then any cost incurred by the Employer will be recoverable.
Key dates are a bit different. They are intended to be a requirement to achieve a certain requirement by a certain date e.g. to provide power to a specific part of the site by a specific date. This is normally to allow the Employer to manage Others (i.e. other 3rd Parties). if the Contractor misses this date for reasons that are their own fault, any resultant cost the Employer incurs as a result will be recoverable from the Contractor (25.3) i.e. undefined/unliquidated cost.
If there is no X7, then outside of the NEC contract the Employer is able to claim unliquidated cost, but if X7 is included it takes away this loophole. If you have X7 and delay damages at say £2000/day, then the fact they have made Completion Date a "key date" which is undefined cost in itself is an "ambiguity". This would actually go against the one who created the ambiguity (which here would be Employer). If the Employers overrun cost will be £25k/month then this should have been identified as the delay damage figure (say £1000/day).
Also worth noting that if the Employer puts delay damages at £2k/day, if they are losing more than that they cant claim any more from the Contractor. Same rule applies to sectional Completion Dates as well.
If there is a genuine key date that the Contractor misses then any cost incurred by the Employer will be recoverable.