How true is this? I'm reading on several sites that your cumulative weekly mileage can be ridden in a single go up to 200-300 miles. As in, if I can regularly do 200 mile weeks, I should be able to do a single 200 mile ride. Anyone put this concept to the test?

According to the training schedule I picked up, it looks like I need to scale back my weekly mileage for a few weeks. That makes me nervous. Like this week, it's saying to do 20 miles midweek, 80 miles Saturday and 20 miles Sunday for 120 miles total. Should I worry about building up too much fatigue if I just plug along with my usual 30-40 mile days 3-4 days a week and add in this long day once a week? The schedule has the long days sea-sawing like: 50, 70, 50, 70, 80, 70, 80, 90, 90, 110, 150, 100, 80, 60, 200 (event day), rest.