Depends on how you are viewing the newsgroups. I use Outlook Express as my
newsreader and there are 2 things I can think of that might casue what you
describe:
1) View>Current View>View Messages by Conversation is NOT checked (this
groups everything by nested thread rather than single posts sorted by date,
subject, poster, etc.)
2) You haven't downloaded all Message Headers. My status bar usually says
something like "987 message(s), 654 unread" It might also say "123 not
downloaded" if I have not downloaded all Headers. Tools>Get Next xxx Headers
fixes that.
If all Headers aren't downloaded you might see a lot of "RE: some subject"
messages.
Depending on what server you are using to connect to the newsgroup, you
might also see a lot of "RE: yada yada" messages because some newsgroup
servers are more thorough than others in passing along or getting updates
(or have differing update schedules).