Let me offer some advice.
Let's say you're using some young women to smuggle Ecstacy into the U.S. from France. Mind you, I'm not saying that's what you're actually doing. Let's just say you're doing it. Allegedly.
You (understandably) want to strike a deal with the United States, which has indicted you. They want a proffer before they'll consider your proposal. You're hesitant, of course. Since you'll be totally implicating yourself. To which you respond by hiring a good attorney, who strikes a written deal that says that the government will not use anything in your proffer at your trial or sentencing.
Sounds good, right?
Except for one thing. You -- and your lawyer -- forgot to add to the deal an agreement not to allow them to turn your proffer over to France. Which then totally uses it to prosecute you there. Which will presumably add a fair piece of additional time to the eight-some years you got in the United States.
Nothing about this worked out very well for you, did it? I at least hope you had some good times when you used your own product (and, potentially, couriers). 'Cause prison's, well, a little bit more of a downer.
Lessons: (1) Make sure the proffer agreement covers any use to anyone. Especially foreign governments, and especially if you've been working there as well. (2) Get yourself an even better lawyer.