Recollections of re-writing a will or scribbling changes to a will after the document has been executed are common. There is a process and procedure to revoking a will. Without the guidance of an experienced estate attorney, a prior and properly executed will trumps a do-it-yourself will.
A recent article from Elder Law Answers, "Efforts to Change Will Using Photocopy and Then Downloaded Form Are Ineffective," describes a case decided by the Minnesota Court of Appeals in August 2015, that proves that it is possible to “fail to revoke” a will.
Esther Sullivan had a will created in 2006. It was a properly executed and valid will that left half of her estate to a former employee. In 2008, she had a change of heart. She photocopied the will and made handwritten changes to it, all of which she initialed. She also wrote that the 2006 will was void. This new document removed the former employee and left half the estate to someone else.