In JBoss Central Software/Updates tab, can select 'show installed' check box and already installed components are shown as disabled (greyed out).

A similar feature should be added to Cordova plug-in Discovery wizard. As at the moment if you have installed a plug-in and then search for it in discovery wizard, the wizard shows nothing to inform you why is isn't listed - user has to make an assumption that it's because they have already installed it rather than say typed the wrong text in the search field.