A car which has not been serviced at the correct intervals, affects to warranty

Hi, I’ve seen an Audi A6 2.0 TDI ULTRA SE. The car was first registered in April 2015 and has had one (company) owner with a mileage at just over 14,000 miles. The dilemma I have is, as the car has not been serviced within the manufacturers warranty guide, the car does not have the residue of the manufacturer’s warranty. The garage has told me that the car was serviced in December 2016 by themselves (not a main dealer) and is quite a long way out of the service requirement, although the mileage is not high.
I believe that this must have quite an adverse affect on the value of the car and I’d be interested in your views regarding this as to how much in per centage terms this could alter the value of the car and what you would consider to be a fair value.