Search Console / SEMRush warned us of URLs that were returning 404 errors on the Rosen & Perry site. URLs could be seen on attorney profiles on external sites.
URLs were similar in structure to what we 301 redirected upon site launch, so we revisited our 301 setup in WPEngine, but everything looked clean.
Turned to Wayback Machine to view the past 2 FindLaw sites. Much of both sites were archived, so I was able to click through and view old pages and their URLs.
The URLs returning 404s were from the FindLaw site from 2 versions ago. We added 301s for all core pages on this site to correct the 404s and scoop up any backlinks that might be pointing to those URLs.