In my case I have an informal and automatic personal killfile program running in my head. Sometimes when I see some particular poster or other I know from experience they are almost certainly not going to be saying anything new, so I simply don't read their more-of-the-same-old. I know this is very very wrong of me, but often I don't have time to read the billionth minor modification of the same basic idea endlessly repeated. I suspect everyone else does the same to some degree, and that this causes a few crossed wires when something new DOES actually come up. So a few wheels get re-invented in any case.

And let me propose a loyal toast to Her Australian Majesty, Queen Elizabeth II, whose official birthday holiday this is in New South Wales, granting me the time to say such things here!