they are by default displayed in increasing order of posting time, and the readers may get bored before reading all replies.
If you do come late, reply to the first post (making some comment about it so it seems like its in the right place) and add something intelligent. This puts your post higher up and more likely to be seen.
OTOH, if people don't check how many votes they use versus how many they have, PM scores bottom post first so the top votes may not be counted. So, the later posts in more recent threads may have a better chance of being hit by Votebots.
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