The NCT is a point in time assessment of a vehicle or more specifically, the testable components of a vehicle, against a set of minimum standard's. It, logically, subjects older cars to a more regular inspection programme than newer cars. It's designed to raise the basic minimum mechanical standard's of the national fleet by withholding a certification that over time will ensure substandard vehicles are removed from the fleet.
The NCT is NOT a certificate of roadworthiness nor a validation of a vehicles current or expected future mechanical state nor does it absolve the owner of their obligation to maintain their vehicle appropriately. To rely on an NCT that was completed 11 months ago or 11 days ago is foolish. Obviously the extended duration gaps between tests were not intended, with the rules designed around incentives etc., as mentioned.
The NCT improves road safety indirectly and over time. It does it's job.