Can I add eventListeners to unsaved documents

Hi, what I'm trying to do is add an eventListener to a document so when I place an image in a box it will check the image name against an applied script label. What I have so far works on documents that have been saved but not on documents that haven't been. However if I open a document that has been saved and then click to the document that hasn't been saved the script then starts working. Can anyone explain what is happening here please?

#targetengine 'ImageCheck'

var doc

var el = app.eventListeners.add("afterActivate", getActive);

function getActive(e){
    if (e.target.constructor.name == "Document") {
        doc = e.target
        try {
        if (!doc.eventListeners.itemByName("afterImportItem").isValid) {
            var afterImportItem = doc.eventListeners.add("afterPlace", checkScriptLabels)
        }
        } catch(e) {}
    }
}