To backfill your goal data, simply create a segment with the same criteria was your goal. For example, let’s say your goal completion location was “thank-you.html” - create a session based segment for page=thank-you.html. The numbers for this segment should be identical to your goal (for the time period since the goal was created.) This is because goals are de-duplicated to 1x/session, so they essentially function the same as a segment.

“But can’t I just use unique pageviews?” Maybe. Unique Pageviews are actually unique based on just on the URL, but also the Page Title. So, let’s say you have multiple regions with a thank-you.hmtl page, but their Page Title is different (“BizWorld USA Confirmation”, “BizWorld DL Confirmation” etc.) These will be considered unique in your Unique Pageviews report, but not in your goal or your segment, since those only care about the URL. So, the most accurate way to backfill goal data is going to be a session-based segment, and using the sessions metric.