With the dent I totally see were you are getting the idea for that but you need to cconsider it like this,
All six helmets were originally dentless they decided to add a dent ,
a dent was made they then made a mold and castings of the dent, and made 5 dents that were to end up in the helmets,
to add the dents they needed to cut out the dent sized hole , it looks as though on the PP2 they went a little to far with the cutting ,
they made the dent with a lip around the out side to blend it in to the rest the PP2 has the most obvious proof tyhe dent was added but if you look closely on the PP3 you can also see were they did this how ever there isnt as much of an extra lip around the dent ,
Any way my point is the dent are all the exact same size and shape they look difrent (specially the ESB) becouse of the added white/light gray highlights on the dent but there all from the same mold