title: Multiple passback tags in single request
body: <p>I need to create passback tags from our Ad Manager account to provide to a parnter. We have about 10 different ad units that are active and 4 different sizes across the different ad units. So, the question is whether I need to give a tag for each ad unit or just one (or two) that covers the different possible sizes? I'm confused as to whether, for example, I need to provide a passback tag specifically for ad unit <code>ad-unit-2</code> that allows for 300x250 or if any 300x250 tag will do the trick.</p>
  <p>So, do I need to provide something like this:</p>
  <pre><code>    window.googletag = window.googletag || {cmd: []};
      googletag.cmd.push(function() {
       googletag.defineSlot('/79xxxxxxxx/ad-unit-1', [300, 250], 'gpt-passback').addService(googletag.pubads());
       googletag.defineSlot('/79xxxxxxxx/ad-unit-2', [728, 90], 'gpt-passback').addService(googletag.pubads());
       googletag.defineSlot('/79xxxxxxxx/ad-unit-3', [300, 100], 'gpt-passback').addService(googletag.pubads());
       googletag.defineSlot('/79xxxxxxxx/ad-unit-4', [300, 250], 'gpt-passback').addService(googletag.pubads());
       googletag.defineSlot('/79xxxxxxxx/ad-unit-5', [300, 250], 'gpt-passback').addService(googletag.pubads());
      googletag.enableServices();
      googletag.display('gpt-passback');
      });
    &lt;/script&gt;
  </code></pre>
  <p>My logic is that in order for a passback ad to show in <code>ad-unit-1</code> I have to provide a tag that specifically mentions that ad unit or if it'll just fill in with anything if I provide a tag of the correct size.</p>
  <p>Something like:</p>
  <pre><code>    window.googletag = window.googletag || {cmd: []};
      googletag.cmd.push(function() {
       googletag.defineSlot('/79xxxxxxxx/ad-unit-1', [300, 250], 'gpt-passback').addService(googletag.pubads());
       googletag.defineSlot('/79xxxxxxxx/ad-unit-2', [728, 90], 'gpt-passback').addService(googletag.pubads());
       googletag.defineSlot('/79xxxxxxxx/ad-unit-3', [300, 100], 'gpt-passback').addService(googletag.pubads());
      googletag.enableServices();
      googletag.display('gpt-passback');
      });
    &lt;/script&gt;
  </code></pre>
  <p>So, would this passback still fill in, say, <code>ad-unit-5</code> (which allows for 300x250) or do I need to specifically include a tag that references <code>ad-unit-5</code>?</p>