Another scenario: if you used an email address that includes your identity for a pseudonymous journal – e.g. johnsmith@gmail.com – just knowing the email for that journal now give your name up as the owner of the journal. Worse, if you used a work or school email, e.g. johnsmith@johnsjob.com or johnsmith@school.edu, this may also betray your institutional affiliation.

For the record, email address of mine that was got in the breach I – coincidentally! – changed on Jan 25, 2014, so that is the last day on which someone could have stolen it from active use on LJ. See https://siderea.dreamwidth.org/1453052.html for discussion. So if we have some reason to believe it happened in 2014, I gather we can narrow it down to the first 25 days of 2014.