This is not the case. The two are distinguishable by specialized tests. Trust me. Even ExGH is detectable, but not currently by any test that can legally be used as 100% proof of use. There are thousands of tests out there, and perhaps the majority cannot distiguish nor from nandrolone, but the good ones can.
Even so, this argument is moot as any sports organization that tests would treat a positive result for both substances equally.