Yeah if you can't locate code you wrote in your own home directory, I dunno what to tell you mate. I'm not here to tell you not to continue your love affair with reverse history search. Do what works for you. All I did was share the easiest way I know to persist a history item as a fn or alias.
Ctrl+R to start reverse search
Type enough to locate last command
Ctrl+X, Ctrl+E to launch command in $EDITOR
Wrap in fn() {} or alias
Save as, or append to some file, e.g. in Vim `:w >> ~/.aliases`