Both the top two are Pomeroy Mark I. The shape of the copper warhead differs quite a lot between individual examples as they were all virtually made by hand. The Mark II Pomeroys are usually found on cases headstamped “VII.A.A.”.
The GB case is quite often found in the unfinished state. Around that time GB did a great deal of work on different extrusion methods and there are all sorts of headstamp variations with different “dots” to indicate different tests. I have a couple of similar unfinished examples myself.
Of course, it could be an unfinished case for a .303 Gerlich, but then again probably not!