Mariel, the rafters, and the ninety miles
1980, 1994, and what a briefly opened door revealed.
What happened
In 1980 Castro opened the port of Mariel and about 125,000 people left in six months, while state-organised crowds attacked the departing at their homes as gusanos — worms. In 1994, after protests in Havana, the coast guard was told to stand aside and roughly 35,000 left on rafts. Both openings were closed again once the scale became clear.
The results
Twice the government briefly opened the door to prove leaving didn't matter, and twice the answer arrived in numbers large enough that the door was shut again.
Why it happened
Cuban departures were treated as treason — property confiscated, return refused, those leaving mobbed by organised crowds. A government that has to punish the act of leaving, and stage hatred of those who go, is telling you exactly what it expects a free count to show. How a system treats the person walking away is the most reliable single measurement you can take of it.