Hi,
Depending on what release you have, you can actually have 3000 announcements (I'm looking at V13)
If you type - change announcment
you will be able to see the first 256 announcements.
if you type instead - cha annoucement 257
you will be able to see announcements from 257 to 512.
basically you can only see your announcements in batches of 256, therefore you have to specify whereabouts in the table of 3000 announcements you want to start looking from.
cheers ash