While it’s an interesting question, I doubt it will become an issue.
I can’t imagine that powers of attorney would even present themselves at an AGM unless there was a “controversial” motion that could affect them.
If it’s a more routine AGM, I doubt you even hear from them. And even if you do, the question will only arise if their vote actually mattered at all. In other words, would it have changed the outcome?
In such hypothetical situations (for a typical AGM that is) it might be best to simply see how it unfolds. It probably will be a non-issue.