I feel as though the marathon schedules that are promoted today are just scaled down versions of what the old top level marathoners did back when marathons first became popular. In those days...runners often did 120-140 miles per week...and more...in order to prepare for marathons. Even top local runners would think nothing of putting in 100+ miles per week. Because of the stress of the training, runners often needed a taper (reduction in training load) that lasted at least several weeks. It took that long to completely recover and rebuild from all the heavy training. Elite marathoners still train this way...for the most part.
Today...many of the marathon training schedules are designed for folks with jobs and time constraints and much more modest goals than those of the professional marathoner. Often these schedule have weekly mileage peaking at 50-55 miles per week. There's nothing wrong with this. The trouble is these schedules often use the same timeline that the elite marathoners use. They start tapering 3-4 weeks out. This is usually too soon for someone training at this level. Instead of tapering, what you end up doing is simply losing fitness.
When I was doing marathons more regularly, I would do 75-85 miles per week. This was a good amount of running, but I really only needed to cut back my long run the week before the race and then pull back my training in the last 3-5 days in order to be fresh and ready to go. Any longer than that and I was flat as a pancake. This was admittedly a pretty short taper but it worked for me.
Here is a good article by Tom Schwartz regarding peaking for the marathon. He makes the interesting observation that endurance oriented runners do better with a short taper while speed oriented runners need a bit longer.
This article by Jeff Gaudette also does a great job of explaining how to avoid tapering too soon...along with a lot more.
If you are dead set on your schedule...don't let any of this throw you. No need to stress. Most training plans will at least have you avoid running too long too close to the race...and that's good. Also, they usually have you ease up on the intensity the last 3-5 days. That's also good. However, you might consider keeping your overall running volume up a bit...especially if you have found yourself flat in previous marathon efforts.
Please use the "Comments" function to ask any questions about your specific situation.
All the best...