At the time of posting this, Twitch says they recycle usernames that have no viewing or login activity for "at least 12 months", which sounds like some usernames will stay longer for reasons unexplained;
and it's unclear if the "batches" being recycled is all usernames that meet the 12 month criteria, or if there is just a day/week/month of the year some undisclosed number of inactive usernames are removed and some 12 month inactive usernames just never make it into those batches;
so I can't tell if a username I want to use that looks inactive is actually 12 months inactive and Twitch decided to let it stay inactive longer than 12 months (or missed it that longs), or if those 12 inactive months haven't passed yet and I can just wait for those 12 months to be up.
There's a username I'd like to change to that only follows 1 channel that hasn't streamed in over 2 years, is not affiliated, and has no VODs or clips; so it appears inactive, but there's an ambiguity as to whether or not anyone has used it in 2 years. And their whisper settings don't allow people to DM them first, so I can't ask them directly for access to that username if they are in fact still active once a year or more.