How to Get the Quantity of Items Invoiced in Magento 1.8

First of all, copying files that can just be overridden from the Core to Local is not best practise as it can possibly give you more work when upgrading Magento.

I have tested your case and found your solution:

First of all I rewrite it in my own extension:

 <models>
            <sales>
                <rewrite><order_pdf_items_invoice_default>MycompanyName_Myextensionname_Model_Order_Pdf_Items_Invoice_Default</order_pdf_items_invoice_default></rewrite>
            </sales>
 </models>

Then I override the function you mentioned above:

 $options = $this->getItemOptions();
    if ($options) {
        foreach ($options as $option) {
            if ($option['value']) {
                if (isset($option['print_value'])) {
                    $_printValue = $option['print_value'];
                } else {
                    $_printValue = strip_tags($option['value']);
                }
                $values = explode(', ', $_printValue);
                foreach ($values as $value) {
                    $lines[][] = array(
                        'text' => Mage::helper('core/string')->str_split(strip_tags($option['label'] . " - " . $value), 40, true, true),
                        'feed' => 40
                    );
                }
            }
        }
    }

What I have done here is just removed the part where you draw the label and added it to the part where you print the value.

If you have long labels/values and you want to keep it on one line, I would increase the value in str_split.

There isn't a built-in way to do this, but there are many paths to the information you want.

This is one of the many ways to do this.

/** @var Mage_Sales_Model_Order $order */
$order = Mage::getModel('sales/order')->load($orderId);

/** @var Mage_Sales_Model_Resource_Order_Item_Collection $items */
$items = Mage::getSingleton('sales/order_item')->getCollection()->setOrderFilter($order);
$items->getSelect()->joinLeft(
    array('oii' => $items->getTable('sales/invoice_item')),
    'main_table.item_id = oii.order_item_id',
    array('invoice_id' => 'parent_id')
);
$items->getSelect()->group('main_table.item_id');

foreach ($items as $item) {
    /** @var Mage_Sales_Model_Order_Item $item */
    $item->setOrder($order);
    if ($item->getInvoiceId()) {
        // Invoiced and this is the invoice number
    } else {
        // Not invoiced (or missing invoice item)
    }
}

You are basically left-joining the invoice items to the order items so you can add the parent_id column from the invoice item as 'invoice_id' when you hydrate the order item record. The 'invoice_id' data will now exist on the order item directly. If there was no matching invoice item then the 'invoice_id' will be null.

I had to directly access the select object as Magento collections do not support a joinLeft directly and if you use the join method on the collection you are doing an inner join which would exclude any order items without matching invoice items.

Lastly, I used the group method on the select to prevent the possibility, however remote, that you get duplicate order items due to the join.

Edit: I updated the way the item collection is gathered because the getItemCollection method on an order is braindead and iterates the order items internally before returning, preventing you from making changes to the collection SQL without doing a reset.