"That would be a quagmire."

Why? I'd have thought running a primary which hadn't been ruled out of order in advance would be a pretty simple thing to do.

Why should there be any need to take into account the defective earlier vote?

How would anybody who had "voted" in the earlier one be "disenfranchised" by being given an opportunity to vote in a fully valid one. Apart from the ones who had died in the meantime, and I'm sure they wouldn't object.