If you want to base it off of visual inspection, I would say if you see a blue label that says KKK Germany and k03 on the turbo then it's most likely the stock turbo.

Others may have a more elegant solution.

 

Thanks for the reply, but I was wondering about something more specific. I wasn't sure if borgwarner keeps track of this somehow.

 

What gives you the suspicion that it is not the original?

 

pop your hood and look at it!