How does vacuum packing affect safe meat storage time?
Vacuum-packing elongates food storage times because by removing the air you remove the oxygen, which aerobic organisms (in this case bacteria) thrive on. No oxygen means no bacterial growth. This is also known as Reduced Oxygen Packaging and can extend freezer life by years.

Some things to keep in mind:


If you open the package, it's life will drop considerably, and you
will be back to a few days tops
If your package fills with air, either the seal broke, or a significant amount of oxygen was trapped inside and bacterial growth is generating decomposition gases. 
If your food provider is a reputable source then their dating is probably accurate. There are significant regulations regarding ROP, and they probably have a production plan that monitors how the food is processed, with dates that are then determined by how the process works.