Why do so many people recommend building PBNs out of dropped domains when they seem so easy for Google to target? Google can easily look at a websites WHOIS data a find the exact date a domain was dropped and re-registered. With this information Google could start just nullifying any backlinks that were created before the re-register date. People who use archive.org recreations are probably the safest. After all it would still have the same content and its possible it had been allowed to expired on accident and re-registered by the same owner, but if a domain gets dropped and simultaneously changes all its content... I can't believe that doesn't throw up red flags at Google and invite more scrutiny.