Easy test for old papers. Just tear a sheet in half, put one half directly in the fix and process the other half as normal. Compare the two halves. To get rid of the fog, add some 2% Benzatriazole solution to your developer. Try 30cc/liter. If that doesn't do the trick try 60cc/liter and so on. Once the fog is gone, try to make a print with the paper and your new "anti-fog" developer.
You can also search for some threads Randy Libersky has written on "Old Paper."
Were it me, I would NOT through this paper out. I once purchased a 500 sheet box of Kodak paper, either Polymax or Fine Art on Ebay. Another photographer sent me a private e-mail and warned me to check to paper for severe fogging. I did, and it was severly fogged. I contacted the retailer and they refunded my $$. I then threw the paper in the trash. I now regret that, because later on that paper could be run through a fix, then used for alternative processes or recoated with another homemade emulsion. I'll never throw out "bad" paper again.
Good Luck,