old_name is a more widely used tag for a previous name: https://wiki.openstreetmap.org/wiki/Key:old_name from the wiki was:name is sometimes used but broader community preference is to use old_name. was:name according to the discussion linked to the wiki also seems to not be picked up by Nominatim. Open to whatever notation you feel is best for the tag if you have a different preference as I dont think going one way or another is a big deal in this case.