I just got home from the Indy 1500 where I purchased a couple handguns. One of which is a new Glock 27 with the NiBX finish. After arriving home I started looking them over. The serial # on the slide and the barrel are the same, but one letter on the receiver serial # is different. The slide and barrel has an A and the receiver has a B. Im confused! Any thoughts will be appreciated. Oh, and the test rounds fired have the receiver serial # on the package. Thanks in advance