Haha, well I should add that I've been testing DOS games for DOSBOX (I'm one of the beta testers) for quite some time and have been through hundereds of games - so far I tested over 800 DOS games on DOSBOX and all but one of the screenshots was among those. And that I've been re-reading old copies of games magazines since 1993
that helps too. But yeah, obscure games could be a problem since those are often even hard to find for download, let alone be well known.