You're joking if you think that this couldn't be scripted to a significant degree.
CNAMEs, where whatever it resolves to is an external site, where the external does not respond to ping or where the external site's WHOIS/ICANN records were updated or created in the last year. Filter out records that match known partners/vendors.
Adjust specifics as makes sense and you cut the problem space significantly. The final steps will still need human verification, but there's no need for this to be manual checks of literal hundreds of records.