If you visit the Members page:
https://vatoto.com/forums/members/
And use the search in the upper-right corner of the page, it will search for members based off of current usernames AND past usernames. As for verifying, you can visit their page and on the right hand side there will be a "Display Name History" button ![:)](https://vatoto.com/forums/public/style_emoticons/default/smile.png)
You mean using
search form instead of "more search options"/"advanced filter options"? It searches through both current display name and one's profile page (i.e. about me section, recent likes given/received, recent threads/posts), but not through name change history.
There apparently is (or should be) something available in Admin CP for such searches, but that's inaccessible to normal members. Combined with Grumpy generally not modifying things that come from IPB, I don't see this suggestion happening. :<
If you have some friends prone to name changes and can't rely on friends list to keep track of them, you could maybe save their profile IDs somewhere? It doesn't change, so unless they create a new account, it'll stick through all name changes and you can just paste it into profile path to get to their profile bypassing any display names they might have. (like yours is 20295, so going to
https://vatoto.com/forums/user/20295-anything will take you to your profile; note: the dash after the number is important; alternatively,
https://vatoto.com/forums/index.php?showuser=20295)