ZcContentDataPlugin.php

    // ----
    public function modifyEntryTableAttributes(&$attributes, $source)
    {
        if ($source == 'zcstalecontent:stale_content')
        {
            unset($attributes['expiryDate']);
            
            // zcContentData is my custom field. It has a Date/Time field and a text field
            // that is grouped into it's own table.
            
            // This is what appears to be the problem:
            // zcContentData is returning an array from my custom field when I want it
            // to return just the date, or $zcContentData['zcDate']
            
            $attributes['zcContentData'] = Craft::t('ZC Date');
        }
    }
    
    // ----
    public function getEntryTableAttributeHtml(EntryModel $entry, $attribute)
    {
        if ($attribute == 'zcContentData')
        {
            // This works. It returns an array from my custom field (zcContentData)
            
            $fieldData = $entry->zcContentData;

            if (!empty($fieldData)) {
                // This works. If the entry has zcContentData then this returns
                // the date specifically.
                return $fieldData['zcDate'];
            }
        }
    }