It is actually a very high serial number...at least for a byf 41... The Germans used a 1 to 4 digit serial followed by a letter suffix... and in the case of a byf 41, it went thru 9999z and then rolled around to 1 thru, somewhere in the XXXXa block prior to the byf 42's... Yours has the E/135 stamp that was applied to all the byf 42's... makes it even a bit more rare...??..or at least to byf collectors it does... Nice gun, best to you, til...lat'r...GT