Notice php by default assume the give string as such format:
'-' is 'y-m-d'
'/' is 'm/d/y'
Unless the given string has Y or M,
that is year is written as full year '2019', or month is written as English shorthand 'Jan',
the default assumption will be applied, where the date might be incorrect.
The following code show a quick test: (true as of php 7.2)
$date = [
'2019-1-3',
'19-1-3',
'3-1-2019',
'3-Jan-19',
'3-1-19', //php assume as y-m-d not d-m-y
'2019-3-1',
'19-3-1',
'1-3-2019',
'1-3-19',
'2019/3/1',
'19/3/1', //fail, php think is month 19
'1/3/2019', //php think is m/d/y
'1/3/19'
];
//Y-M-d
foreach($date as $i => $d){
echo $i ."\r\n";
var_dump(date_format(date_create($d), 'Y-M-d'));
echo "\r\n";
}