Collective2 allows only "go-forward results." We require that you begin a new trading strategy on Collective2 and start building a track record from this point in time. The point is that you need to commit publicly to revealing your track record, and then you can begin sending trade signals to C2. If we allowed people to import old trade histories, they would only choose the good histories, not the bad, and thus the results would be skewed and incorrectly represented.
However, it is perfectly fine if you want to describe your back-history results in your strategy description on your C2 system page.