Would attaching a notarized statement be sufficient to correct an error to my advance medical directive paperwork?

Are witnesses necessary?

My notarized statement will be as follows: To Whom It May Concern: I just discovered that there was a typographical error in my Advance Medical Directive. dated Month Day Year. On page 2, the name " Jane Doe" as my attorney-in-fact(Agent) should have read “John Doe”. This error was obviously an oversight. The same word file was used for my husband's Advance Medical Directive, where I am named as his attorney-in-fact. When the word file was used to generate my Advance Medical Directive, the preparer overlooked to change the name to my husband, John Doe. The attorney who prepared the Advance Medical Directive , had passed away several years ago.

Signed:Jane Doe