Some geolocation databases have a category for proxies, for instance MaxMind uses the A1 code for the "country" Anonymous Proxyhttps://dev.maxmind.com/geoip/legacy/codes/iso3166/

(Of course, these categorizations would need to be accurate (both proxy detection and country detection) to get meaningful results)

I find your consideration that proxy IP addresses are invalid strange, though. Maybe considering just edits that were not reverted would be a more useful metric?