Yes that's the case. To get enough data we probably need lots of in vitro experiments. Remember that data is not equal to information - even really big sample sizes wouldn't be enough to resolve the combinatoric explosion. What I mean in that comment up there (I posted it before it was finished, I think) is that there are ~23k genes in the genome, so even under the absurdly simple assumption that there's only one mutation possible per gene, you have half a billion possible combinations of gene breakages, which you will never ever be able to get enough of a sample size to look at blindly.