It can be added to a collection also as long as the 'always show title bar' in settings>display is checked. Just press the pencil icon at the top left which brings up the edit song page. Click on the collection and select the additional entries. It's just like doing the first/original song edit.
Dell Latitude 13.5" 2-in-1 Ubuntu/Win 11
Samsung Note Pro SM-P900 12.2 Android 5.0.2
Samsung S7+, Android 12
Samsung Note Pro SM-P900 12.2 Android 5.0.2
Samsung S7+, Android 12