By default XenForo username search fields (example: Find member) only finds members if they have been active with the past 180 days. This add-on overcomes this limit by searching all usernames.
Please note this add-on may not be suitable if you have tens of thousands of members.
(Example of Find member block in Members page)
Questions and answers:
Q: Do add-on which have username search fields benefit from this add-on?