How do I view a history of usernames and/or passwords for a site?
Select the pencil icon to the right of the site entry in your LastPass Online Vault at https://lastpass.com/ or Local Vault via the browser extension.
In the "Edit Site Information" dialog, select "[ History ]" located under to the password or username fields. A new dialog will appear with a recorded history of that username or password. -- If you're unable to locate a "history" link, there has been no password or username changes saved to LastPass.