So H is called H on the basis for Dot tapping 4 times as he died?
Not quite.
In the dying declaration, Dot was asked to blink on the first letter of the Big Bent Copper's name and he blinked on H. Whilst also tapping his fingers (spotted later by Steve) and construed as dot, dot, dot, dot
So could the person's name begin with H, well yes quite possibly. Or not, if there are four like Dot that who need to be rooted out. But what does 'like Dot' mean? Main assumption is any OCG bent copper/official; there have however been oodles of those, but you can narrow it down to those what are acting more of their own volition than because of coercion
Another theory is that 'Dot' refers to someone who have been deliberately infiltrated into the police by the OCG - and that we saw in S1 Hilton commissioning one, presumably the 4th to join, Ryan. The other two being Dot and Jo (who shows just how long the OCG has been around and how long a game they'll play)
TL:DR - we don't know exact significance.
But there are still Bent Coppers to be found out.
But will Big Bent Bastard off anyone in AC12 (Kate has survived, for now at least). Because surely they'd want rid of straight coppers who thwart their activities in general or are coming close to the worst (child sex abuse, trafficking).
How far do we think they recruited Hastings in S2?