I was going off of [this](https://github.com/maxmind/geoip-api-python/blob/master/py_GeoIP.c#L321) line in Maxmind's official python wrapper, which does `!= REV0`. Their C-API explicitly [checks for `GEOIP_CITY_EDITION_REV1`](https://github.com/maxmind/geoip-api-c/blob/master/libGeoIP/GeoIPCity.c#L152), though. Ostensibly Maxmind will continue to support metro code and area code in newer revisions, so I think it makes sense to do `!= REV0` instead of an explicit check.