date
returns a string but you are using integers in the switch
statement. Use:
case '01':
$dateY = date('Y')+1;
break;
etc.
However, the switch code can be much simpler, and there is no need to call the date function again since dateY has already been initialised in advance:
switch($dateM)
{
case '01':
case '02':
case '03':
case '04':
case '05':
case '06':
$dateY+=1;
}
And even simpler, you can skip the switch altogether:
if(intval($dateM) < 7) $dateY+=1;