enigma1 - 1:07 pm on Mar 23, 2012 (gmt 0)
Yes seems like they never drop them. I see accesses for years now on ancient links and even if they don't exist elsewhere google still keeps a record.
The problem with serving the "highly relevant alternatives" is that you cannot tell in advance the kind of requests many of them artificial putting stretch on the server doing various queries to find suggestions. A redirect path filters many of them, if done correctly it can put the visitor to the nearest page relevant to the request made.