The nature of these damaged files is usually of 2 origins:
1) DMCA takedown( nowadays it is mostly HBO shows + console games on Highwinds(newshosting,usenetserver newsdemon etc) & Giganews(supernews\powerusenet etc) servers(check resellers list) )
2) Technical glithes (Astraweb is infamous for these ones. At the moment there is a ~200 days range affected( files uploaded ~200-350 days ago )
Whatever the cause,upon finding lots of incomplete files one shouldnt switch immediately to another NNTP provider.Every single one of them has its cons and pros and one might just trade bad for worse.
A proper servers' setup will most definitely help to reduce or in most cases eliminate the nasty issue of damaged files.
Proper Servers' Setup For SABnzbd
Assuming you use SABnzbd and Astraweb's main server is EU
This setup will do wonders with any usenet provider.
Server 1: Astraweb EU
-enabled
Server 2: XSusenet (free server)
-enabled
-connections=2
-retention=400
-optional or backup*
Server 3: Astraweb US
-enabled
-optional or backup*
Server 4: Blocknews (100 gb block account $15)
-enabled
-backup server
* SABnzbd cant set preference levels for servers so having xsusenet & AW US and blocknews as backup servers might result in downloading articles first from blocknews sometimes.And we wouldnt want that since xsusenet is free & AW US is unlimited.
This is why i think its better to set xsusenet & AW US as optional servers, not backup with 2 & 2 connections each.But it all depends on sabnzbd behaviour.If setting them up as backup works OK for you then dont make them optional