I don't know about the enforcement/evidence, but the end of the original link sheds some light, sounds like they have a pretty mature process for trying to hand

I don't know about the enforcement/evidence, but the end of the original link sheds some light, sounds like they have a pretty mature process for trying to handle illegitimate requests: > we try to catch erroneous or abusive removal requests.... [examples of bad requests]... We try to catch these ourselves, but we also notify webmasters in our Webmaster Tools when pages on their website have been targeted by a copyright removal request, so that they can submit a counter-notice if they believe the removal request was inaccurate.