If true, I wouldn’t get so excited about the “implications” of this other than further evidence that Joe’s cognitive decline is real, and progressing.
Barring a tearful public confession, if the guy claims that is his mark, it’s his mark. It has the full effect of it being authentic until not just proven that it isn’t his mark, but also proven that Joe couldn’t/didn’t approve of his mark being used.
At this point, I’m expecting a checkmark.