please don't oversimplify...bone fragments offer much more evidence than simply the carbon that's in them...i'm sure you know this though. i suppose you're refering to carbon-dating...a little different isn't it? carbon dating doesn't tell you that it's carbon from a hominid...only how old the sample is...the fact that it's from a hominid is determined by other methods(anthropology), not the carbon-dating...what other methods are used in irms testing to tell us that the carbon in question comes from syntyhetic T, and not somewhere else?
i really am interested if you've got the patience...
I suggest you look through some past threads, if they're still around. This was discussed very thoroughly after Floyd's positive was announced around the end of July, 06, and particularly after his documents became available online, I think in October of that year. Also Don Catlin's 2001 article on using IRMS for this purpose, try a search with his name, testosterone and doping.
Carbon ratios don't tell you it's carbon from a T-metabolite, either, that's determined by chromatographic elution profiles, together with mass spectometry. Again, this is discussed exhaustively in some of the old threads.