Each airline has its own preferences regarding the release of information, i no for certain that all airlines operating to/from Cork, do not release any passenger figures until after the flight has arrived @ the Destination Airport, the's figures are then made available to the public & OCC as soon as the flight is detected arrived at its destination airport, by CFMU - EuroControl.
As for what law it falls under im not sure, but i think it may be under the passenger manifests act , i think that's available in the IAA Navigation Acts & Law Book.