However, if the node title shows that all three posts came from the same person/IP address I personally would decide that none of them are genuine and not bother replying.
This anon troll typically posts replies. You already know from previous posts that this is a troll, and you don't need to reply.
Do you really think there are people who think "I'm going to reply, oh, no, he may be a troll, I don't know from this posts, but lets browse through old posts and see if there's a matching IP address"? Come on. Half of the people on Perlmonks can't even read the post they are replying to carefully - people aren't going to remember IP addresses, or bother to do crossmatching. And even if half the people on PM do, it's still not going to work - the other half will create the troll droppings.
Anonymonks monks having their IP addresses listed aren't really anonymous, are they?
though I still don't understand, and nobody AFAICS has tried to explain, what the big deal is about creating an unofficial "anonymous" login if one needs that
What's an unofficial "anonymous" login
? And, whatever it is, what's keeping trolls from creating it?
Linking trolls with anonymous monks is like saying "See, there's a notorious driver around who often drives too fast around schools. And he's driving a red car. Let's equip all red cars with a siren, so we know he's coming".