The `unread_not_too_old` attribute is a little odd because there should never be a case where
the user's first_unread_at column is less than the `Topic#updated_at`
column of an unread topic. The `unread_not_too_old` attribute is causing
a bug where topic states synced into `TopicTrackingState` do not appear
as unread because the attribute does not exsist on a normal `Topic`
object and hence never set.
Alan Guo Xiang Tan