Astraweb's retention is 160 days, growing over time (although not yet it seems) to 270 days.
Your Log contains very precise information about what exactly Alt.Binz has downloaded, and what it can't download - look for 'Article not found' messages, this means too old for your server typically. Obviously Alt.Binz can only download what's on your server.
The % completion that shows in your queue has nothing to do with whether *you* can actually grab it, it only shows the completion on the server that the indexing site used when it added the header info to its database. In Newzleech's case, this means Giganews. People can use any server to download, so unless you actually check the headers on your own server yourself, there's no way of knowing with Alt.Binz whether it's downloadable until you actually try to download it - because Alt.Binz doesn't handle headers at all.
Edit: but, just in case this wasn't clear, use your server's published retention as a guide, and don't try to download anything older than 160 days (yet) and you should be fine.