In short
Coverage closure falls behind when the rate of new coverage drops below what is needed to finish by the date. That is visible weeks before the milestone is missed, if the trend is compared with the date every day instead of being reported as a percentage each week.
Why is a coverage percentage misleading?
A block at 87% coverage sounds nearly finished. Whether it is depends on the slope: if it gained ten points last month and one point this month, the last 13% may take longer than everything before it. The percentage reports where you are. The slope reports whether you will arrive.
What is the early signal?
The day the projected closure date passes the milestone date. On a real program that signal appeared 104 days before samples. It was noted, a request for two more engineers was deferred, and the program eventually missed by seventeen days.
What should an alarm include?
More than the trend:
- What it blocks next: usually integration, then firmware, then samples.
- What is slowing it: flaky tests, open defects, or simply too few people.
- The options, while adding capacity would still work.
How Tymeline handles it
Tymeline reads regression results directly and forecasts closure against the date daily. When the trend stops reaching the date, it raises the alarm that day and shows what the delay would block downstream.