Well, what value are you getting? I mentioned that I'm getting 273.
Try mktime() instead. Example:
$thing = '2005-10-01';
$month = (int) substr($thing, 5, 2);
$day = (int) substr($thing, 8, 2);
$year = (int) substr($thing, 0, 4);
// or do: list($year, $month, $day) = explode('-', $thing);
$storedDate = date('z', mktime(0, 0, 0, $month, $day, $year));
echo $storedDate;
🙂