Pulling a GPC variable

[Dr.CustUmz]

I am working on a product, building from previously existing products, this is a page within the admincp.
I am wondering why sometimes I am able to pull a GPC variable and other times I am not, I am having this issue in multiple spots but this is just the smallest one to give the example.

I am able to pull the productid with:

PHP Code:

$vbulletin->GPC['productid'] 


But I cant get the catid to pull:

PHP Code:

$vbulletin->GPC['catid'] 


This is the complete page in question, Just a simple confirmation page.

PHP Code:

$vbulletin->input->clean_array_gpc('r', array(
  'productid' => TYPE_UINT,
  'catid' => TYPE_UINT
));

print_form_header('digigacp', 'dodeleteproduct');

construct_hidden_code('s', $vbulletin->session->vars['sessionhash']);
construct_hidden_code('adminhash', ADMINHASH);
construct_hidden_code('productid', $vbulletin->GPC['productid']);
construct_hidden_code('catid', $vbulletin->GPC['catid']);

print_table_header($vbphrase['confirm']);
print_description_row($vbphrase['are_you_sure']);
print_description_row('Product ID: ' . intval($vbulletin->GPC['productid']));
print_description_row('Category: ' . intval($vbulletin->GPC['catid']));
print_submit_row($vbphrase['yes'], '', 2, $vbphrase['no']); 


A way I get around this is to use a query, but since I can pull the productid, I just dont understand why I cant pull the catid, when they were both submitted through the same form.

This is how I currently solve this problem:

PHP Code:

$vbulletin->input->clean_array_gpc('r', array(
        'productid' => TYPE_UINT,
        'catid' => TYPE_UINT
    ));
  
  $info = $db->query_first("SELECT catid
    FROM " . TABLE_PREFIX . "products
    WHERE productid = " . intval($vbulletin->GPC['productid']) . "
  ");

    print_form_header('digigacp', 'dodeleteproduct');
    construct_hidden_code('s', $vbulletin->session->vars['sessionhash']);
    construct_hidden_code('adminhash', ADMINHASH);

    construct_hidden_code('productid', $vbulletin->GPC['productid']);
    construct_hidden_code('catid', $vbulletin->GPC['catid']);
    print_table_header($vbphrase['confirm']);
    print_description_row($vbphrase['are_you_sure']);
  print_description_row('Product ID: ' . intval($vbulletin->GPC['productid']));
  print_description_row('Category: ' . $info['catid']);
    print_submit_row($vbphrase['yes'], '', 2, $vbphrase['no']);