2 or 3 positions depends on the size of the post, the smaller sizes only take two.
Could be a genuine post with aftermarket unmarked holders.
Its hardly surprising that the aftermarket ones vary in fit when even the drawings posted in this thread have differing dimensions
Of the 20plus holders I have only 4 are originals but they all seem to fit, the last few needed a bit of encouragement but at about £10 each fair enough. Anyone tried a Bison one on a Dickson post?