There's a script:
for($i=80; $i<=89; $i++)
{
$date = '01.04.19'.$i;
$intlDateFormatter = new \IntlDateFormatter('ru', 2, -1, 'Europe/Moscow', 1, 'dd.MM.yyyy');
$intlDateFormatter->setLenient(false);
$timestamp = $intlDateFormatter->parse($date);
echo $date . ' = ' . var_export($timestamp, 1);
echo '<br>' . PHP_EOL;
}
And script outputs:
01.04.1980 = 323384400
01.04.1981 = false
01.04.1982 = false
01.04.1983 = false
01.04.1984 = false
01.04.1985 = 481147200
01.04.1986 = 512683200
01.04.1987 = 544219200
01.04.1988 = 575841600
01.04.1989 = 607377600
What's wrong with dates: 01.04.1981, 01.04.1982, 01.04.1983, 01.04.1984? PHP 5.5.9-1