Bren serial numbers.

[Peter Laidler]

Guns were sidelined on a regular basis for on-line faults and diverted to a rectification or hospital bay. If the gun could be made serviceable all well and good, it was sent on its way at the relevant place on the production line so to speak. Some of those that could only be made serviceable with selectively fitted parts were skeletonised by apprentices or made into the earliest DP guns while others had an A suffix added to the serial number as in H-1234/A as an indication of this to Armourers

So if you have one with an A suffix, that's the reason. If you have a ZZ suffix to the serial number, then that's something else. And DPB, then that's something else too!