It occurred to me that most HM & FM plans fill the time between starting the plan and the event itself. One consequence of this is that if anything interrupts that (perhaps a cold or a minor sprain) then training won't be completed on time. Do you think it would make sense to add some consolidation time in to the middle of the plan?
For example, on a FM plan, maybe getting to 18 miles then spending a month doing a weekly long run around 18 miles (probably better to drop some of them to 12 or 10) before completing the rest of the plan. That way, if there are any delays earlier on, they can be absorbed by cutting back on the consolidation.