|Could this have been prevented by proper conduct by a notary?|
First, it appears that the notary didn't have the person posing as Mr. Williams personally appear and have his ID examined. But I'm wondering if the ex-wife just claimed that her signature was the only one that the notary needed to notarize that day. I know... Pure speculation, but there are lots of different possibilities. And this example could relate to the fairly recent thread here about completion of all the details (including specifying pronouns) in a notary certificate. Also, lining out any remaining space where names are to be filled in, might also prevent potential tampering.
We have no idea if this was the case here or not, but it could be a good lesson in prevention for notaries everywhere on why and how details can make a difference.