Personally I don't feel courses degrade over "time". There is nothing about the passing of time that invalidates the initial measurement. There are events that occur that alter the course, but those events could occur the day after the measurement or 10 years later. Time period itself is irrelevant, so the thought that some magical time period governs the course validity really makes no sense.
So courses shouldn't "expire" based on time. Uncertainty doesn't "creep in", it shows up with a road grader at totally random intervals. Courses don't get over ripe through gradual deterioration, they are either destroyed in an instant or remain undisturbed.
So the question of "life events" affecting a course should be asked every time results are submitted, and active courses without life events should never expire. Those with those events expire immediately and require recertification. The only place a time period has any value is to keep the list clean, no results come in, after 3-4 years the course should go inactive and require recertification. If people don't submit results then their courses expire quickly.