Unless I'm mistaken, this is all driven off the initial date? Is that appropriate? If a service is done late, should the next service of that type be done on the original schedule, or x weeks after it was last done? In my world, it would be the latter. If oil changes are scheduled to be done every 4k miles, and they're late doing the first one and do it at 6k, we don't want the next done at 8k. It will be done 4k after the last, at 10k (and somebody will get chewed on for doing the first late ).