Slot Window Compliance
On the CFMU portal, there's a graphic that shows "Slot Window Compliance". The current pie chart is fairly typical:
Complied 1045 (57%)
Dep. before 492 (27%)
Dep. after 295 (16%)
Am I misunderstanding what this means? The poor compliance percentage surprises me, as I thought that ATC would enforce the slot robustly, not permitting t/o before the slot, and requiring a DLA to be sent (precipitating a probable later slot) if the aircraft didn't make it away by the end of the slot. What's the real life practice?