This site has pretty good information. It doesn't mention the fat being skimmed off, so I would say that you can subtract a gram or two of fat (and the corresponding 9-18 calories) per cup, if you want. Without actually having the specific stock tested in a laboratory, that's as accurate as you're likely to get. You can always measure the fat that you skim off in an attempt to be more exact, but it's likely to contain other components as well.
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