You have to open it to be 100% but that's risky with famicom carts. I haven't gotten around to trying it but weighing it and comparing to other known good carts with the same pcb should be a good indicator. Eproms make a cart heavier and modern counterfeits use smaller boards and lighter flash chips.yours looks pretty legit though so I wouldn't worry too much if you can't do any other checks right now.