Personally, I wouldn’t blink an eye for a vehicle that oil change receipts are provided for anywhere between 6500 and 9500 miles over the life of the vehicle, if the vehicle was a highway cruiser, with a long commute.
My '07 Altima and I typically went between 5k and 9500 miles between oil changes, depending on conditions. If I was doing a long road trip (like from Denver to NYC and back, which I did a couple of times), then the oil changes went longer.
I changed the oil myself every single time, and it was never low when I checked it every 1k miles, and not low when I would change it out. I kept a sample of each oil drain, and sent off a bunch of them for testing, and still have some sitting on my shelf to be tested if I feel like it currently.
I popped the valve cover off at the 50k mile mark, and everything was clean as a whistle inside.
So, trying to say that long oil changes lead to sludge problems is not a guarantee in all cases.
You guys really should change your thinking to allow for reality to come into play.
Now, if I lived in NYC with my Altima, and drove under those conditions, I wouldn’t have run my oil changes that long. More like 4k miles at the most. But, that’s the variability you have to take into consideration.
I traded my car in at 58k miles, and it was running fine, clean as a whistle, and I provided all my receipts and oil analysis reports when I swapped cars. I even went into carfax, and updated their information with all my oil change history as a previous owner of the car, which helped it sell.