Unquestionably, there are also many instances where
the systems fails and
where lots of copyrighted material gets uploaded. Back in 2005, we had a
case similar to the one you described in German Wikipedia, where various
IPs copied content from old books. It is a big mess to clean up, but it can
be done. And luckily the cases of massive copyvios are quite rare.
For further information see
https://de.wikipedia.org/wiki/Wikipedia:Archiv/DDR-URV/Presseinfo (German).
Cheers
Martin