Jason, your line-up of the 42 dated receivers is interesting. The receiver on the far left is a byf receiver. With your photography being excellent, I have changed my mind. At first, I suggested it was a Banner receiver, but it is not.
The other three shown are correctly described. I'm with Vlim regarding what happened to this Luger. It was made to function and as far a Mauser corporate was concerned, the rest didn't matter. Maybe it ended up in some police department and had the sear safety added. It would appear so. The funky grips are not correct, as has been mentioned. Where and when the Su4 mag came on the scene is another unknown. Send it back, or shoot it. It won't hurt to take it to the range and enjoy it. Best, Jim