That's always a tricky one - and if one of the group threads you mention includes Pixie then I've been thinking the same thing! Two-way threads are always easier because you can just PM the person in question. I sort of think that, of it's been a couple of months in a thread that formerly had a reply every few days, it's okay to claim.
Of course, if it picks up again there's no penalty, you just won't be able to claim any further posts there
