can you see older sessions or are all sessions older than 3 months not visible in the restore? how are you doing the restore. in dp gui under restore, do you browse it within "restore objects" or "restore session". Because if you use restore objects per default it shows only versions from the last 3 months. you can change that in the dropdown "search interval"
if you just cant see just this one restore session, maybe the catalog protection was set not long enough or the session was manually removed. then you have to re-import the media from the corresponding backup session
