If it is (1) dated (2) signed and all in the deceased's own handwriting it is a valid "holographic" will. Your facts seem to indicate it is not dated. If not a valid holographic will, two witnesses are necessary but not notarization.
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Under the right circumstances a fairly "casual" note that's signed and dated can be admitted as a will ... as long as it's entirely in your own handwriting. It can be on the back of an envelope if it says "this is my will. Give all my property to (name)." .. I got one like that admitted to probate a number of years ago.
BUT, it would be better if the will were more formal - that way, it's less likely to be challenged. And since there are no "do-overs" after you're gone, if it's important to you that your assets go to the people (or organizations) you want them to go to, then it should be important to you to do it right.
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If it is not in your own handwriting, it does not qualify as a holographic Will. It would then need to meet all requirements for a formal Will, which your note probably does not. If all of the beneficiaries are in agreement, (Including the ONE beneficiary from the old Will), you might be able to have the note admitted to probate. Otherwise, I think it will be tossed out.
This is one of the MANY MANY examples why it is so critical to see an attorney to get your estate planning done right. Otherwise, whatever you leave behind might totally fail to realize your objectives and your wishes and intent will be thwarted. Estate planning is not a do-it-yourself project!
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