The chart is not confusing and is quite precise (see below).

As an example, if you are not in Y, between the US and Europe, you would ordinarily be permitted one bag at 50 lbs. As a Medallion, you get one more bag without charge (which would ordinarily cost $100). Note that this does not include overweight charges on either bag. For each bag between 51-70 lbs, you pay an extra $100:

http://www.delta.com/content/www/en_...p/checked.html