The directory is updated every week. If the congregation is not there it is not ELCA
Besides that, if a Lutheran parish has a website, and it is part of the ELCA, it usually proudly posts that fact (compete with the ELCA logo) on the website.
Since it is becoming less and less a point of pride to be part of the ELCA (except for the most “progressive” parishes), that might change, however. Use the ELCA “find a congregation” directory.
Our Orthodox parish got itself a new Catechumen last Sunday, with three more expected this Sunday. The latter three (a father with his two little girls—his wife is more hesitant) came from an ELCA parish that was going entirely wacko, with “gays” and dance liturgies.
Glory to God for all things!!!!