My theory is that some of these troll threads are sort of real.
For example: my ExH dumped me nearly 25 years ago. There was an upsetting miscarriage in the mix too. There was no internet then, he had a car phone but there were not the mobiles we have now or the technology. I was convinced there was someone else but he strenuously denied it. Ah well. Now I have my lovely DH and 3 wonderful DCs - so what about that twat. Yet when I read stuff about "the script" I think, Aaargh, that is SO ExH! Wish I had had Mumsnet then. And I wonder how it would have panned out if I had been able to ask for advice.
So I wonder if, were I not happy now, if life had not worked out for me and I was still miserable and heartbroken after all those years, whether I might be tempted to start a thread and pretend it is all happening now. As a way of working things through, getting closure perhaps. To get confirmation of what I suspected.
And if I were to do that, after all this time certain things would not ring true. For example, when I miscarried, I rang the GPs and the Doctor came round and called an ambulance for me.
That just wouldn't happen today and that would get people's trolldar flashing. And I wouldn't be able to check his phone because he only had a carphone, so I would have to make up an excuse or be vague about what phone he had, which would also arouse suspicions. And the thread would probably move much faster than the events did at the time. And if posters said "when you see him say/do this" I wouldn't, because I couldn't, because it was 25 years ago.
And that is what I think some people are doing. Especially the losing twins people - I think they might have lost babies in the past and can't get over it and are trying to get someone to talk to about their grief when everyone in real life has forgotten about it.
I must say at this point that I have never started a troll thread looking for sympathy. (I was responsible for a v successful funny one back in the day when it was acceptable to do funny troll threads, almost a rite of passage, but that's it, honest). I haven't needed to but I think there are people who do need to and that's why their threads don't ring true.