A number of suspicious guests still reaching old or buried threads is definitely something worth looking at, though. There will always be edge cases, especially with bots that behave more like normal browsers or arrive through old indexed URLs, external links, archives, bookmarks, or previously discovered URLs.
I am also planning additional detection features that should help with exactly this type of behaviour, including deliberately placed hidden/trap URLs that normal users should never reach, but crawlers and scrapers often will. That should give Bot Guard another strong signal for identifying bots that currently appear more human-like.