Hi I have been around cars many years and never been a fan of extended service intervals that are north of 10k, I am privileged to know a few car engineers who work for manufacturers one of whom took me as a guest to an engine oil producers main testing lab for their products, the one thing I learned was that modern engine oil is far better than say twenty years ago but the common denominator is the oil turning black, a lot of this is carbon which the oil suspends to render it harmless, this carbon which is abrasive in oils having done over 10k will start to become critical so imagine that lot in another 9k on top, better to have lots of services and a non worn engine, far better selling point, in essence if you can't do the service at 9k and it runs 1500 miles past no big deal.
Steve.