How far back I go really depends on how much time I have at that particular sitting. When I have more time I will go back a couple of weeks and answer posts that have been sitting unanswered for that length of time.
But normally I go back to the last post of the previous day and work forward to the first and last today.
I hate to see a post go unanswered and mostly one will do this if we do not have a qualified person to answer that particular post, then I will jump on out of curtesy and answer it stating I am not qualified in this area, but here it goes.
I think its like someone saying HI and you not responding. It may get that person back to us.