We just published some results about the use transaction malleability in the Bitcoin network with a special focus on MtGox:
In this work we use traces of the Bitcoin network for over a year preceding the filing to show that[...]
Although I'm sure your conclusion is correct, if you only examined a year's worth of data that doesn't conclusively prove there was no TM loss. Results for previous years would likely be the same, but we can't just assume that.