The data collected over the years clearly confirm a depletion of ozone in the stratosphere. what do scientists still need to learn about the ozone hole?

In recent years the hole in ozone layer has been observed to be shrinking from previous years. In the past, when the hole was discovered they did not yet know what was the cause of the depletion. Since they have discovered the culprits as certain chemical found in aerosols and refrigerants, they have since  banned or reduced the use of these chemicals and as such the depleted layer has started to recover.